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 $62.57   7.248%   $67.1051   $67.11   $67.10   $67.10  
  Purchase #2 $202.78   12.368%   $227.8598   $227.86   $227.85   $227.90  
  Purchase #3 $51.77   13.205%   $58.6062   $58.61   $58.60   $58.60  
  Purchase #4 $202.39   7.552%   $217.6745   $217.67   $217.65   $217.70  
  Purchase #5 $41.82   9.435%   $45.7657   $45.77   $45.75   $45.80  
  Purchase #6 $242.77   11.210%   $269.9845   $269.98   $270.00   $270.00  
  Purchase #7 $41.63   6.380%   $44.286   $44.29   $44.30   $44.30  
  7 purchase totals = $845.73       $931.2818   $931.29   $931.25   $931.40