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 $187.53   7.194%   $201.0209   $201.02   $201.00   $201.00  
  Purchase #2 $36.42   12.497%   $40.9714   $40.97   $40.95   $41.00  
  Purchase #3 $115.70   6.478%   $123.195   $123.20   $123.20   $123.20  
  Purchase #4 $199.41   13.216%   $225.764   $225.76   $225.75   $225.80  
  Purchase #5 $139.87   9.609%   $153.3101   $153.31   $153.30   $153.30  
  Purchase #6 $27.35   3.387%   $28.2763   $28.28   $28.30   $28.30  
  Purchase #7 $143.97   6.118%   $152.7781   $152.78   $152.80   $152.80  
  7 purchase totals = $850.25       $925.3158   $925.32   $925.30   $925.40