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 $23.84   7.431%   $25.6116   $25.61   $25.60   $25.60  
  Purchase #2 $212.31   8.195%   $229.7088   $229.71   $229.70   $229.70  
  Purchase #3 $169.41   4.426%   $176.9081   $176.91   $176.90   $176.90  
  Purchase #4 $37.94   3.156%   $39.1374   $39.14   $39.15   $39.10  
  Purchase #5 $241.67   3.272%   $249.5774   $249.58   $249.60   $249.60  
  Purchase #6 $174.68   11.668%   $195.0617   $195.06   $195.05   $195.10  
  Purchase #7 $111.44   13.513%   $126.4989   $126.50   $126.50   $126.50  
  7 purchase totals = $971.29       $1,042.5039   $1,042.51   $1,042.50   $1,042.50