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 $187.73   8.128%   $202.9887   $202.99   $203.00   $203.00  
  Purchase #2 $96.42   8.539%   $104.6533   $104.65   $104.65   $104.70  
  Purchase #3 $76.54   9.418%   $83.7485   $83.75   $83.75   $83.70  
  Purchase #4 $64.79   12.469%   $72.8687   $72.87   $72.85   $72.90  
  Purchase #5 $196.91   11.467%   $219.4897   $219.49   $219.50   $219.50  
  Purchase #6 $106.89   10.258%   $117.8548   $117.85   $117.85   $117.90  
  Purchase #7 $104.49   10.353%   $115.3078   $115.31   $115.30   $115.30  
  7 purchase totals = $833.77       $916.9115   $916.91   $916.90   $917.00