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 $127.93   13.601%   $145.3298   $145.33   $145.35   $145.30  
  Purchase #2 $14.73   12.355%   $16.5499   $16.55   $16.55   $16.50  
  Purchase #3 $200.37   7.122%   $214.6404   $214.64   $214.65   $214.60  
  Purchase #4 $229.51   5.226%   $241.5042   $241.50   $241.50   $241.50  
  Purchase #5 $129.81   11.693%   $144.9887   $144.99   $145.00   $145.00  
  Purchase #6 $160.27   9.582%   $175.6271   $175.63   $175.65   $175.60  
  Purchase #7 $90.34   6.141%   $95.8878   $95.89   $95.90   $95.90  
  7 purchase totals = $952.96       $1,034.5279   $1,034.53   $1,034.60   $1,034.40