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 $241.96   13.793%   $275.3335   $275.33   $275.35   $275.30  
  Purchase #2 $55.31   12.182%   $62.0479   $62.05   $62.05   $62.00  
  Purchase #3 $143.62   5.138%   $150.9992   $151.00   $151.00   $151.00  
  Purchase #4 $241.87   8.167%   $261.6235   $261.62   $261.60   $261.60  
  Purchase #5 $28.64   10.660%   $31.693   $31.69   $31.70   $31.70  
  Purchase #6 $46.60   13.327%   $52.8104   $52.81   $52.80   $52.80  
  Purchase #7 $237.26   8.657%   $257.7996   $257.80   $257.80   $257.80  
  7 purchase totals = $995.26       $1,092.3071   $1,092.30   $1,092.30   $1,092.20