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 $227.73   6.154%   $241.7445   $241.74   $241.75   $241.70  
  Purchase #2 $171.84   13.258%   $194.6225   $194.62   $194.60   $194.60  
  Purchase #3 $35.73   9.858%   $39.2523   $39.25   $39.25   $39.30  
  Purchase #4 $169.43   11.788%   $189.4024   $189.40   $189.40   $189.40  
  Purchase #5 $65.51   8.354%   $70.9827   $70.98   $71.00   $71.00  
  Purchase #6 $245.29   6.430%   $261.0621   $261.06   $261.05   $261.10  
  Purchase #7 $107.58   8.489%   $116.7125   $116.71   $116.70   $116.70  
  7 purchase totals = $1,023.11       $1,113.7790   $1,113.76   $1,113.75   $1,113.80