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 $192.34   4.511%   $201.0165   $201.02   $201.00   $201.00  
  Purchase #2 $22.89   8.183%   $24.7631   $24.76   $24.75   $24.80  
  Purchase #3 $168.59   3.467%   $174.435   $174.44   $174.45   $174.40  
  Purchase #4 $135.57   5.237%   $142.6698   $142.67   $142.65   $142.70  
  Purchase #5 $118.77   12.806%   $133.9797   $133.98   $134.00   $134.00  
  Purchase #6 $81.83   8.412%   $88.7135   $88.71   $88.70   $88.70  
  Purchase #7 $60.45   6.172%   $64.181   $64.18   $64.20   $64.20  
  7 purchase totals = $780.44       $829.7586   $829.76   $829.75   $829.80