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 $209.72   12.758%   $236.4761   $236.48   $236.50   $236.50  
  Purchase #2 $147.91   10.415%   $163.3148   $163.31   $163.30   $163.30  
  Purchase #3 $59.27   13.238%   $67.1162   $67.12   $67.10   $67.10  
  Purchase #4 $212.37   3.386%   $219.5608   $219.56   $219.55   $219.60  
  Purchase #5 $176.48   10.449%   $194.9204   $194.92   $194.90   $194.90  
  Purchase #6 $208.90   13.199%   $236.4727   $236.47   $236.45   $236.50  
  Purchase #7 $159.36   12.540%   $179.3437   $179.34   $179.35   $179.30  
  7 purchase totals = $1,174.01       $1,297.2047   $1,297.20   $1,297.15   $1,297.20