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 $75.32   12.515%   $84.7463   $84.75   $84.75   $84.70  
  Purchase #2 $124.96   10.409%   $137.9671   $137.97   $137.95   $138.00  
  Purchase #3 $234.53   5.787%   $248.1023   $248.10   $248.10   $248.10  
  Purchase #4 $60.95   13.105%   $68.9375   $68.94   $68.95   $68.90  
  Purchase #5 $95.97   13.667%   $109.0862   $109.09   $109.10   $109.10  
  Purchase #6 $248.54   6.452%   $264.5758   $264.58   $264.60   $264.60  
  Purchase #7 $99.83   13.271%   $113.0784   $113.08   $113.10   $113.10  
  7 purchase totals = $940.10       $1,026.4936   $1,026.51   $1,026.55   $1,026.50