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 $61.96   9.569%   $67.889   $67.89   $67.90   $67.90  
  Purchase #2 $13.79   5.305%   $14.5216   $14.52   $14.50   $14.50  
  Purchase #3 $139.35   13.171%   $157.7038   $157.70   $157.70   $157.70  
  Purchase #4 $150.41   11.343%   $167.471   $167.47   $167.45   $167.50  
  Purchase #5 $28.78   7.422%   $30.9161   $30.92   $30.90   $30.90  
  Purchase #6 $95.84   9.142%   $104.6017   $104.60   $104.60   $104.60  
  Purchase #7 $126.98   10.529%   $140.3497   $140.35   $140.35   $140.30  
  7 purchase totals = $617.11       $683.4529   $683.45   $683.40   $683.40