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 $60.45   4.587%   $63.2228   $63.22   $63.20   $63.20  
  Purchase #2 $226.99   13.738%   $258.1739   $258.17   $258.15   $258.20  
  Purchase #3 $35.92   10.614%   $39.7325   $39.73   $39.75   $39.70  
  Purchase #4 $157.88   10.328%   $174.1858   $174.19   $174.20   $174.20  
  Purchase #5 $244.97   9.463%   $268.1515   $268.15   $268.15   $268.20  
  Purchase #6 $232.73   4.242%   $242.6024   $242.60   $242.60   $242.60  
  Purchase #7 $18.51   10.523%   $20.4578   $20.46   $20.45   $20.50  
  7 purchase totals = $977.45       $1,066.5267   $1,066.52   $1,066.50   $1,066.60