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 $60.28   12.283%   $67.6842   $67.68   $67.70   $67.70  
  Purchase #2 $242.67   10.592%   $268.3736   $268.37   $268.35   $268.40  
  Purchase #3 $248.93   9.145%   $271.6946   $271.69   $271.70   $271.70  
  Purchase #4 $243.40   3.112%   $250.9746   $250.97   $250.95   $251.00  
  Purchase #5 $149.80   4.813%   $157.0099   $157.01   $157.00   $157.00  
  Purchase #6 $249.64   4.353%   $260.5068   $260.51   $260.50   $260.50  
  Purchase #7 $57.84   11.399%   $64.4332   $64.43   $64.45   $64.40  
  7 purchase totals = $1,252.56       $1,340.6769   $1,340.66   $1,340.65   $1,340.70