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 $188.93   7.259%   $202.6444   $202.64   $202.65   $202.60  
  Purchase #2 $176.66   9.142%   $192.8103   $192.81   $192.80   $192.80  
  Purchase #3 $35.53   11.121%   $39.4813   $39.48   $39.50   $39.50  
  Purchase #4 $93.46   11.598%   $104.2995   $104.30   $104.30   $104.30  
  Purchase #5 $53.49   8.765%   $58.1784   $58.18   $58.20   $58.20  
  Purchase #6 $244.75   3.428%   $253.14   $253.14   $253.15   $253.10  
  Purchase #7 $207.37   6.150%   $220.1233   $220.12   $220.10   $220.10  
  7 purchase totals = $1,000.19       $1,070.6772   $1,070.67   $1,070.70   $1,070.60