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 $233.72   9.496%   $255.9141   $255.91   $255.90   $255.90  
  Purchase #2 $194.57   3.596%   $201.5667   $201.57   $201.55   $201.60  
  Purchase #3 $194.78   7.289%   $208.9775   $208.98   $209.00   $209.00  
  Purchase #4 $93.85   4.191%   $97.7833   $97.78   $97.80   $97.80  
  Purchase #5 $179.66   6.165%   $190.736   $190.74   $190.75   $190.70  
  Purchase #6 $9.72   3.214%   $10.0324   $10.03   $10.05   $10.00  
  Purchase #7 $153.94   4.741%   $161.2383   $161.24   $161.25   $161.20  
  7 purchase totals = $1,060.24       $1,126.2483   $1,126.25   $1,126.30   $1,126.20