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 $95.71   8.669%   $104.0071   $104.01   $104.00   $104.00  
  Purchase #2 $47.31   11.781%   $52.8836   $52.88   $52.90   $52.90  
  Purchase #3 $115.95   8.608%   $125.931   $125.93   $125.95   $125.90  
  Purchase #4 $134.93   10.115%   $148.5782   $148.58   $148.60   $148.60  
  Purchase #5 $118.31   7.771%   $127.5039   $127.50   $127.50   $127.50  
  Purchase #6 $60.32   6.600%   $64.3011   $64.30   $64.30   $64.30  
  Purchase #7 $123.33   6.207%   $130.9851   $130.99   $131.00   $131.00  
  7 purchase totals = $695.86       $754.1900   $754.19   $754.25   $754.20