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 $126.54   8.343%   $137.0972   $137.10   $137.10   $137.10  
  Purchase #2 $139.78   12.323%   $157.0051   $157.01   $157.00   $157.00  
  Purchase #3 $213.46   12.764%   $240.706   $240.71   $240.70   $240.70  
  Purchase #4 $225.90   8.776%   $245.725   $245.73   $245.75   $245.70  
  Purchase #5 $233.31   7.433%   $250.6519   $250.65   $250.65   $250.70  
  Purchase #6 $137.63   9.229%   $150.3319   $150.33   $150.35   $150.30  
  Purchase #7 $78.52   8.468%   $85.1691   $85.17   $85.15   $85.20  
  7 purchase totals = $1,155.14       $1,266.6862   $1,266.70   $1,266.70   $1,266.70