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 $222.93   6.257%   $236.8787   $236.88   $236.90   $236.90  
  Purchase #2 $58.62   12.241%   $65.7957   $65.80   $65.80   $65.80  
  Purchase #3 $111.89   12.157%   $125.4925   $125.49   $125.50   $125.50  
  Purchase #4 $151.78   13.653%   $172.5025   $172.50   $172.50   $172.50  
  Purchase #5 $214.51   7.125%   $229.7938   $229.79   $229.80   $229.80  
  Purchase #6 $131.30   11.654%   $146.6017   $146.60   $146.60   $146.60  
  Purchase #7 $50.50   8.853%   $54.9708   $54.97   $54.95   $55.00  
  7 purchase totals = $941.53       $1,032.0357   $1,032.03   $1,032.05   $1,032.10