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 $40.69   6.533%   $43.3483   $43.35   $43.35   $43.30  
  Purchase #2 $189.57   11.566%   $211.4957   $211.50   $211.50   $211.50  
  Purchase #3 $158.37   12.201%   $177.6927   $177.69   $177.70   $177.70  
  Purchase #4 $82.39   12.115%   $92.3715   $92.37   $92.35   $92.40  
  Purchase #5 $233.29   4.273%   $243.2585   $243.26   $243.25   $243.30  
  Purchase #6 $85.25   12.427%   $95.844   $95.84   $95.85   $95.80  
  Purchase #7 $69.67   9.584%   $76.3472   $76.35   $76.35   $76.30  
  7 purchase totals = $859.23       $940.3579   $940.36   $940.35   $940.30