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 $88.53   9.347%   $96.8049   $96.80   $96.80   $96.80  
  Purchase #2 $149.74   6.821%   $159.9538   $159.95   $159.95   $160.00  
  Purchase #3 $6.48   10.140%   $7.1371   $7.14   $7.15   $7.10  
  Purchase #4 $114.81   7.786%   $123.7491   $123.75   $123.75   $123.70  
  Purchase #5 $91.88   10.113%   $101.1718   $101.17   $101.15   $101.20  
  Purchase #6 $124.71   6.281%   $132.543   $132.54   $132.55   $132.50  
  Purchase #7 $250.32   9.370%   $273.775   $273.78   $273.80   $273.80  
  7 purchase totals = $826.47       $895.1347   $895.13   $895.15   $895.10