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 $243.86   9.693%   $267.4973   $267.50   $267.50   $267.50  
  Purchase #2 $238.73   13.359%   $270.6219   $270.62   $270.60   $270.60  
  Purchase #3 $152.42   10.429%   $168.3159   $168.32   $168.30   $168.30  
  Purchase #4 $235.93   11.729%   $263.6022   $263.60   $263.60   $263.60  
  Purchase #5 $104.58   8.333%   $113.2947   $113.29   $113.30   $113.30  
  Purchase #6 $85.91   8.859%   $93.5208   $93.52   $93.50   $93.50  
  Purchase #7 $114.81   5.644%   $121.2899   $121.29   $121.30   $121.30  
  7 purchase totals = $1,176.24       $1,298.1427   $1,298.14   $1,298.10   $1,298.10