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 $58.99   6.477%   $62.8108   $62.81   $62.80   $62.80  
  Purchase #2 $182.87   11.224%   $203.3953   $203.40   $203.40   $203.40  
  Purchase #3 $222.34   9.372%   $243.1777   $243.18   $243.20   $243.20  
  Purchase #4 $203.32   8.831%   $221.2752   $221.28   $221.30   $221.30  
  Purchase #5 $29.39   10.497%   $32.4751   $32.48   $32.50   $32.50  
  Purchase #6 $167.79   5.400%   $176.8507   $176.85   $176.85   $176.90  
  Purchase #7 $28.32   6.578%   $30.1829   $30.18   $30.20   $30.20  
  7 purchase totals = $893.02       $970.1677   $970.18   $970.25   $970.30