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 $185.45   9.422%   $202.9231   $202.92   $202.90   $202.90  
  Purchase #2 $132.67   5.107%   $139.4455   $139.45   $139.45   $139.40  
  Purchase #3 $121.83   9.828%   $133.8035   $133.80   $133.80   $133.80  
  Purchase #4 $242.76   7.418%   $260.7679   $260.77   $260.75   $260.80  
  Purchase #5 $156.80   5.551%   $165.504   $165.50   $165.50   $165.50  
  Purchase #6 $135.51   11.399%   $150.9568   $150.96   $150.95   $151.00  
  Purchase #7 $175.88   9.814%   $193.1409   $193.14   $193.15   $193.10  
  7 purchase totals = $1,150.90       $1,246.5417   $1,246.54   $1,246.50   $1,246.50