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 $106.65   11.773%   $119.2059   $119.21   $119.20   $119.20  
  Purchase #2 $114.54   13.846%   $130.3992   $130.40   $130.40   $130.40  
  Purchase #3 $146.32   3.562%   $151.5319   $151.53   $151.55   $151.50  
  Purchase #4 $216.47   11.334%   $241.0047   $241.00   $241.00   $241.00  
  Purchase #5 $59.86   3.513%   $61.9629   $61.96   $61.95   $62.00  
  Purchase #6 $71.59   12.416%   $80.4786   $80.48   $80.50   $80.50  
  Purchase #7 $83.69   10.612%   $92.5712   $92.57   $92.55   $92.60  
  7 purchase totals = $799.12       $877.1544   $877.15   $877.15   $877.20