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 $126.42   10.113%   $139.2049   $139.20   $139.20   $139.20  
  Purchase #2 $21.82   7.559%   $23.4694   $23.47   $23.45   $23.50  
  Purchase #3 $116.35   10.122%   $128.1269   $128.13   $128.15   $128.10  
  Purchase #4 $180.28   12.118%   $202.1263   $202.13   $202.15   $202.10  
  Purchase #5 $168.53   11.163%   $187.343   $187.34   $187.35   $187.30  
  Purchase #6 $179.78   5.164%   $189.0638   $189.06   $189.05   $189.10  
  Purchase #7 $129.84   9.217%   $141.8074   $141.81   $141.80   $141.80  
  7 purchase totals = $923.02       $1,011.1417   $1,011.14   $1,011.15   $1,011.10