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 $107.77   6.112%   $114.3569   $114.36   $114.35   $114.40  
  Purchase #2 $61.78   5.552%   $65.21   $65.21   $65.20   $65.20  
  Purchase #3 $107.84   8.736%   $117.2609   $117.26   $117.25   $117.30  
  Purchase #4 $64.55   6.847%   $68.9697   $68.97   $68.95   $69.00  
  Purchase #5 $86.66   7.317%   $93.0009   $93.00   $93.00   $93.00  
  Purchase #6 $240.93   8.314%   $260.9609   $260.96   $260.95   $261.00  
  Purchase #7 $14.91   5.751%   $15.7675   $15.77   $15.75   $15.80  
  7 purchase totals = $684.44       $735.5268   $735.53   $735.45   $735.70