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 $192.30   4.748%   $201.4304   $201.43   $201.45   $201.40  
  Purchase #2 $161.56   12.273%   $181.3883   $181.39   $181.40   $181.40  
  Purchase #3 $76.26   6.381%   $81.1262   $81.13   $81.15   $81.10  
  Purchase #4 $238.43   6.223%   $253.2675   $253.27   $253.25   $253.30  
  Purchase #5 $149.45   4.807%   $156.6341   $156.63   $156.65   $156.60  
  Purchase #6 $86.33   13.343%   $97.849   $97.85   $97.85   $97.80  
  Purchase #7 $27.72   7.515%   $29.8032   $29.80   $29.80   $29.80  
  7 purchase totals = $932.05       $1,001.4987   $1,001.50   $1,001.55   $1,001.40