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 $33.47   4.587%   $35.0053   $35.01   $35.00   $35.00  
  Purchase #2 $122.94   5.744%   $130.0017   $130.00   $130.00   $130.00  
  Purchase #3 $8.36   11.251%   $9.3006   $9.30   $9.30   $9.30  
  Purchase #4 $209.76   11.461%   $233.8006   $233.80   $233.80   $233.80  
  Purchase #5 $25.59   13.752%   $29.1091   $29.11   $29.10   $29.10  
  Purchase #6 $243.69   12.197%   $273.4129   $273.41   $273.40   $273.40  
  Purchase #7 $89.77   7.730%   $96.7092   $96.71   $96.70   $96.70  
  7 purchase totals = $733.58       $807.3394   $807.34   $807.30   $807.30