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 $183.42   8.831%   $199.6178   $199.62   $199.60   $199.60  
  Purchase #2 $241.25   9.838%   $264.9842   $264.98   $265.00   $265.00  
  Purchase #3 $171.78   12.540%   $193.3212   $193.32   $193.30   $193.30  
  Purchase #4 $57.28   4.746%   $59.9985   $60.00   $60.00   $60.00  
  Purchase #5 $250.46   12.588%   $281.9879   $281.99   $282.00   $282.00  
  Purchase #6 $150.26   13.255%   $170.177   $170.18   $170.20   $170.20  
  Purchase #7 $85.50   13.704%   $97.2169   $97.22   $97.20   $97.20  
  7 purchase totals = $1,139.95       $1,267.3035   $1,267.31   $1,267.30   $1,267.30