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 $23.87   4.676%   $24.9862   $24.99   $25.00   $25.00  
  Purchase #2 $99.94   8.692%   $108.6268   $108.63   $108.65   $108.60  
  Purchase #3 $167.38   13.184%   $189.4474   $189.45   $189.45   $189.40  
  Purchase #4 $206.36   8.308%   $223.5044   $223.50   $223.50   $223.50  
  Purchase #5 $167.45   4.470%   $174.935   $174.94   $174.95   $174.90  
  Purchase #6 $70.59   5.702%   $74.615   $74.62   $74.60   $74.60  
  Purchase #7 $209.40   7.513%   $225.1322   $225.13   $225.15   $225.10  
  7 purchase totals = $944.99       $1,021.2470   $1,021.26   $1,021.30   $1,021.10