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 $111.73   8.858%   $121.627   $121.63   $121.65   $121.60  
  Purchase #2 $209.96   8.421%   $227.6407   $227.64   $227.65   $227.60  
  Purchase #3 $95.80   3.756%   $99.3982   $99.40   $99.40   $99.40  
  Purchase #4 $217.36   4.849%   $227.8998   $227.90   $227.90   $227.90  
  Purchase #5 $229.26   8.103%   $247.8369   $247.84   $247.85   $247.80  
  Purchase #6 $165.51   12.862%   $186.7979   $186.80   $186.80   $186.80  
  Purchase #7 $225.77   11.634%   $252.0361   $252.04   $252.05   $252.00  
  7 purchase totals = $1,255.39       $1,363.2366   $1,363.25   $1,363.30   $1,363.10