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 $84.33   11.171%   $93.7505   $93.75   $93.75   $93.80  
  Purchase #2 $190.42   3.759%   $197.5779   $197.58   $197.60   $197.60  
  Purchase #3 $162.94   10.561%   $180.1481   $180.15   $180.15   $180.10  
  Purchase #4 $250.76   13.402%   $284.3669   $284.37   $284.35   $284.40  
  Purchase #5 $76.76   10.716%   $84.9856   $84.99   $85.00   $85.00  
  Purchase #6 $87.59   4.639%   $91.6533   $91.65   $91.65   $91.70  
  Purchase #7 $90.51   12.132%   $101.4907   $101.49   $101.50   $101.50  
  7 purchase totals = $943.31       $1,033.9730   $1,033.98   $1,034.00   $1,034.10