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 $182.62   12.114%   $204.7426   $204.74   $204.75   $204.70  
  Purchase #2 $81.29   13.864%   $92.56   $92.56   $92.55   $92.60  
  Purchase #3 $157.48   10.381%   $173.828   $173.83   $173.85   $173.80  
  Purchase #4 $176.64   9.591%   $193.5815   $193.58   $193.60   $193.60  
  Purchase #5 $242.44   12.181%   $271.9716   $271.97   $271.95   $272.00  
  Purchase #6 $136.56   4.744%   $143.0384   $143.04   $143.05   $143.00  
  Purchase #7 $42.44   8.427%   $46.0164   $46.02   $46.00   $46.00  
  7 purchase totals = $1,019.47       $1,125.7385   $1,125.74   $1,125.75   $1,125.70