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 $217.28   12.177%   $243.7382   $243.74   $243.75   $243.70  
  Purchase #2 $90.97   9.499%   $99.6112   $99.61   $99.60   $99.60  
  Purchase #3 $199.26   8.223%   $215.6451   $215.65   $215.65   $215.60  
  Purchase #4 $97.33   9.190%   $106.2746   $106.27   $106.25   $106.30  
  Purchase #5 $198.67   5.431%   $209.4598   $209.46   $209.45   $209.50  
  Purchase #6 $147.76   7.350%   $158.6204   $158.62   $158.60   $158.60  
  Purchase #7 $156.46   9.717%   $171.6632   $171.66   $171.65   $171.70  
  7 purchase totals = $1,107.73       $1,205.0125   $1,205.01   $1,204.95   $1,205.00