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 $243.91   4.550%   $255.0079   $255.01   $255.00   $255.00  
  Purchase #2 $41.29   8.703%   $44.8835   $44.88   $44.90   $44.90  
  Purchase #3 $87.97   4.479%   $91.9102   $91.91   $91.90   $91.90  
  Purchase #4 $23.69   7.646%   $25.5013   $25.50   $25.50   $25.50  
  Purchase #5 $115.27   8.623%   $125.2097   $125.21   $125.20   $125.20  
  Purchase #6 $195.50   3.651%   $202.6377   $202.64   $202.65   $202.60  
  Purchase #7 $162.33   11.539%   $181.0613   $181.06   $181.05   $181.10  
  7 purchase totals = $869.96       $926.2116   $926.21   $926.20   $926.20