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 $54.38   12.480%   $61.1666   $61.17   $61.15   $61.20  
  Purchase #2 $207.43   6.320%   $220.5396   $220.54   $220.55   $220.50  
  Purchase #3 $206.36   11.580%   $230.2565   $230.26   $230.25   $230.30  
  Purchase #4 $192.91   3.284%   $199.2452   $199.25   $199.25   $199.20  
  Purchase #5 $238.40   10.597%   $263.6632   $263.66   $263.65   $263.70  
  Purchase #6 $19.99   11.227%   $22.2343   $22.23   $22.25   $22.20  
  Purchase #7 $189.54   11.742%   $211.7958   $211.80   $211.80   $211.80  
  7 purchase totals = $1,109.01       $1,208.9012   $1,208.91   $1,208.90   $1,208.90