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 $167.92   7.659%   $180.781   $180.78   $180.80   $180.80  
  Purchase #2 $215.91   13.352%   $244.7383   $244.74   $244.75   $244.70  
  Purchase #3 $13.42   8.644%   $14.58   $14.58   $14.60   $14.60  
  Purchase #4 $133.27   7.205%   $142.8721   $142.87   $142.85   $142.90  
  Purchase #5 $169.85   5.484%   $179.1646   $179.16   $179.15   $179.20  
  Purchase #6 $85.77   10.232%   $94.546   $94.55   $94.55   $94.50  
  Purchase #7 $183.50   5.517%   $193.6237   $193.62   $193.60   $193.60  
  7 purchase totals = $969.64       $1,050.3057   $1,050.30   $1,050.30   $1,050.30