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 $86.84   8.811%   $94.4915   $94.49   $94.50   $94.50  
  Purchase #2 $199.41   3.329%   $206.0484   $206.05   $206.05   $206.00  
  Purchase #3 $123.88   4.695%   $129.6962   $129.70   $129.70   $129.70  
  Purchase #4 $217.47   4.374%   $226.9821   $226.98   $227.00   $227.00  
  Purchase #5 $112.89   4.747%   $118.2489   $118.25   $118.25   $118.20  
  Purchase #6 $200.62   3.103%   $206.8452   $206.85   $206.85   $206.80  
  Purchase #7 $77.74   8.761%   $84.5508   $84.55   $84.55   $84.60  
  7 purchase totals = $1,018.85       $1,066.8631   $1,066.87   $1,066.90   $1,066.80