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 $64.82   12.258%   $72.7656   $72.77   $72.75   $72.80  
  Purchase #2 $179.42   5.787%   $189.803   $189.80   $189.80   $189.80  
  Purchase #3 $175.71   10.705%   $194.5198   $194.52   $194.50   $194.50  
  Purchase #4 $108.38   13.189%   $122.6742   $122.67   $122.65   $122.70  
  Purchase #5 $187.56   7.119%   $200.9124   $200.91   $200.90   $200.90  
  Purchase #6 $232.97   12.292%   $261.6067   $261.61   $261.60   $261.60  
  Purchase #7 $102.68   6.132%   $108.9763   $108.98   $109.00   $109.00  
  7 purchase totals = $1,051.54       $1,151.2580   $1,151.26   $1,151.20   $1,151.30