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 $212.78   9.845%   $233.7282   $233.73   $233.75   $233.70  
  Purchase #2 $211.51   11.716%   $236.2905   $236.29   $236.30   $236.30  
  Purchase #3 $143.52   11.666%   $160.263   $160.26   $160.25   $160.30  
  Purchase #4 $169.87   9.209%   $185.5133   $185.51   $185.50   $185.50  
  Purchase #5 $102.61   6.431%   $109.2088   $109.21   $109.20   $109.20  
  Purchase #6 $161.35   9.417%   $176.5443   $176.54   $176.55   $176.50  
  Purchase #7 $25.56   4.627%   $26.7427   $26.74   $26.75   $26.70  
  7 purchase totals = $1,027.20       $1,128.2908   $1,128.28   $1,128.30   $1,128.20