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 $61.35   11.699%   $68.5273   $68.53   $68.55   $68.50  
  Purchase #2 $150.80   9.763%   $165.5226   $165.52   $165.50   $165.50  
  Purchase #3 $141.26   4.317%   $147.3582   $147.36   $147.35   $147.40  
  Purchase #4 $245.43   5.303%   $258.4452   $258.45   $258.45   $258.40  
  Purchase #5 $78.98   7.842%   $85.1736   $85.17   $85.15   $85.20  
  Purchase #6 $149.97   4.762%   $157.1116   $157.11   $157.10   $157.10  
  Purchase #7 $70.77   4.406%   $73.8881   $73.89   $73.90   $73.90  
  7 purchase totals = $898.56       $956.0266   $956.03   $956.00   $956.00