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 $85.98   9.659%   $94.2848   $94.28   $94.30   $94.30  
  Purchase #2 $110.42   4.398%   $115.2763   $115.28   $115.30   $115.30  
  Purchase #3 $17.94   5.327%   $18.8957   $18.90   $18.90   $18.90  
  Purchase #4 $247.92   13.255%   $280.7818   $280.78   $280.80   $280.80  
  Purchase #5 $71.48   3.668%   $74.1019   $74.10   $74.10   $74.10  
  Purchase #6 $155.73   12.171%   $174.6839   $174.68   $174.70   $174.70  
  Purchase #7 $168.68   13.633%   $191.6761   $191.68   $191.70   $191.70  
  7 purchase totals = $858.15       $949.7005   $949.70   $949.80   $949.80