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 $177.26   11.723%   $198.0402   $198.04   $198.05   $198.00  
  Purchase #2 $87.96   4.426%   $91.8531   $91.85   $91.85   $91.90  
  Purchase #3 $237.95   7.104%   $254.854   $254.85   $254.85   $254.90  
  Purchase #4 $184.84   13.258%   $209.3461   $209.35   $209.35   $209.30  
  Purchase #5 $110.68   7.255%   $118.7098   $118.71   $118.70   $118.70  
  Purchase #6 $40.82   13.265%   $46.2348   $46.23   $46.25   $46.20  
  Purchase #7 $244.27   13.341%   $276.8581   $276.86   $276.85   $276.90  
  7 purchase totals = $1,083.78       $1,195.8961   $1,195.89   $1,195.90   $1,195.90