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 $55.67   6.576%   $59.3309   $59.33   $59.35   $59.30  
  Purchase #2 $161.73   4.273%   $168.6407   $168.64   $168.65   $168.60  
  Purchase #3 $121.91   11.731%   $136.2113   $136.21   $136.20   $136.20  
  Purchase #4 $123.48   3.754%   $128.1154   $128.12   $128.10   $128.10  
  Purchase #5 $55.57   13.442%   $63.0397   $63.04   $63.05   $63.00  
  Purchase #6 $197.55   10.157%   $217.6152   $217.62   $217.60   $217.60  
  Purchase #7 $168.30   12.767%   $189.7869   $189.79   $189.80   $189.80  
  7 purchase totals = $884.21       $962.7401   $962.75   $962.75   $962.60