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 $101.58   3.853%   $105.4939   $105.49   $105.50   $105.50  
  Purchase #2 $81.63   7.166%   $87.4796   $87.48   $87.50   $87.50  
  Purchase #3 $100.81   10.115%   $111.0069   $111.01   $111.00   $111.00  
  Purchase #4 $129.52   3.260%   $133.7424   $133.74   $133.75   $133.70  
  Purchase #5 $142.36   9.464%   $155.833   $155.83   $155.85   $155.80  
  Purchase #6 $39.34   6.813%   $42.0202   $42.02   $42.00   $42.00  
  Purchase #7 $172.25   12.190%   $193.2473   $193.25   $193.25   $193.20  
  7 purchase totals = $767.49       $828.8233   $828.82   $828.85   $828.70