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 $173.77   11.687%   $194.0785   $194.08   $194.10   $194.10  
  Purchase #2 $119.65   12.604%   $134.7307   $134.73   $134.75   $134.70  
  Purchase #3 $202.62   4.565%   $211.8696   $211.87   $211.85   $211.90  
  Purchase #4 $127.56   3.616%   $132.1726   $132.17   $132.15   $132.20  
  Purchase #5 $38.65   7.381%   $41.5028   $41.50   $41.50   $41.50  
  Purchase #6 $197.89   7.691%   $213.1097   $213.11   $213.10   $213.10  
  Purchase #7 $51.27   5.227%   $53.9499   $53.95   $53.95   $53.90  
  7 purchase totals = $911.41       $981.4138   $981.41   $981.40   $981.40