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 $192.80   5.149%   $202.7273   $202.73   $202.75   $202.70  
  Purchase #2 $217.54   11.716%   $243.027   $243.03   $243.05   $243.00  
  Purchase #3 $204.49   7.857%   $220.5568   $220.56   $220.55   $220.60  
  Purchase #4 $67.86   5.209%   $71.3948   $71.39   $71.40   $71.40  
  Purchase #5 $27.94   11.334%   $31.1067   $31.11   $31.10   $31.10  
  Purchase #6 $126.92   4.404%   $132.5096   $132.51   $132.50   $132.50  
  Purchase #7 $112.55   9.746%   $123.5191   $123.52   $123.50   $123.50  
  7 purchase totals = $950.10       $1,024.8413   $1,024.85   $1,024.85   $1,024.80