Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $112.48   13.345%   $127.4905   $127.49   $127.50   $127.50  
  Purchase #2 $215.85   11.756%   $241.2253   $241.23   $241.25   $241.20  
  Purchase #3 $58.98   11.835%   $65.9603   $65.96   $65.95   $66.00  
  Purchase #4 $125.57   3.161%   $129.5393   $129.54   $129.55   $129.50  
  Purchase #5 $219.30   11.309%   $244.1006   $244.10   $244.10   $244.10  
  Purchase #6 $201.64   8.818%   $219.4206   $219.42   $219.40   $219.40  
  Purchase #7 $167.85   10.607%   $185.6538   $185.65   $185.65   $185.70  
  7 purchase totals = $1,101.67       $1,213.3904   $1,213.39   $1,213.40   $1,213.40