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 $58.31   11.861%   $65.2261   $65.23   $65.25   $65.20  
  Purchase #2 $125.70   12.147%   $140.9688   $140.97   $140.95   $141.00  
  Purchase #3 $122.54   4.239%   $127.7345   $127.73   $127.75   $127.70  
  Purchase #4 $150.55   3.488%   $155.8012   $155.80   $155.80   $155.80  
  Purchase #5 $79.51   5.320%   $83.7399   $83.74   $83.75   $83.70  
  Purchase #6 $14.35   13.731%   $16.3204   $16.32   $16.30   $16.30  
  Purchase #7 $141.38   4.669%   $147.981   $147.98   $148.00   $148.00  
  7 purchase totals = $692.34       $737.7719   $737.77   $737.80   $737.70