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 $236.54   13.162%   $267.6734   $267.67   $267.65   $267.70  
  Purchase #2 $61.41   6.827%   $65.6025   $65.60   $65.60   $65.60  
  Purchase #3 $111.50   9.657%   $122.2676   $122.27   $122.25   $122.30  
  Purchase #4 $68.37   13.586%   $77.6587   $77.66   $77.65   $77.70  
  Purchase #5 $191.78   12.854%   $216.4314   $216.43   $216.45   $216.40  
  Purchase #6 $234.71   9.570%   $257.1717   $257.17   $257.15   $257.20  
  Purchase #7 $231.95   10.573%   $256.4741   $256.47   $256.45   $256.50  
  7 purchase totals = $1,136.26       $1,263.2794   $1,263.27   $1,263.20   $1,263.40