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 $228.35   6.754%   $243.7728   $243.77   $243.75   $243.80  
  Purchase #2 $196.45   12.257%   $220.5289   $220.53   $220.55   $220.50  
  Purchase #3 $106.32   5.465%   $112.1304   $112.13   $112.15   $112.10  
  Purchase #4 $78.89   11.274%   $87.7841   $87.78   $87.80   $87.80  
  Purchase #5 $195.85   3.229%   $202.174   $202.17   $202.15   $202.20  
  Purchase #6 $155.68   11.316%   $173.2967   $173.30   $173.30   $173.30  
  Purchase #7 $6.83   13.329%   $7.7404   $7.74   $7.75   $7.70  
  7 purchase totals = $968.37       $1,047.4273   $1,047.42   $1,047.45   $1,047.40