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 $149.66   12.216%   $167.9425   $167.94   $167.95   $167.90  
  Purchase #2 $162.47   7.674%   $174.9379   $174.94   $174.95   $174.90  
  Purchase #3 $99.53   13.188%   $112.656   $112.66   $112.65   $112.70  
  Purchase #4 $45.69   4.334%   $47.6702   $47.67   $47.65   $47.70  
  Purchase #5 $206.82   3.754%   $214.584   $214.58   $214.60   $214.60  
  Purchase #6 $226.59   13.825%   $257.9161   $257.92   $257.90   $257.90  
  Purchase #7 $246.35   8.485%   $267.2528   $267.25   $267.25   $267.30  
  7 purchase totals = $1,137.11       $1,242.9595   $1,242.96   $1,242.95   $1,243.00