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 $238.86   12.301%   $268.2422   $268.24   $268.25   $268.20  
  Purchase #2 $62.87   9.290%   $68.7106   $68.71   $68.70   $68.70  
  Purchase #3 $9.75   13.803%   $11.0958   $11.10   $11.10   $11.10  
  Purchase #4 $117.89   3.829%   $122.404   $122.40   $122.40   $122.40  
  Purchase #5 $152.28   9.286%   $166.4207   $166.42   $166.40   $166.40  
  Purchase #6 $236.46   11.511%   $263.6789   $263.68   $263.70   $263.70  
  Purchase #7 $95.70   4.203%   $99.7223   $99.72   $99.70   $99.70  
  7 purchase totals = $913.81       $1,000.2745   $1,000.27   $1,000.25   $1,000.20