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 $7.96   12.385%   $8.9458   $8.95   $8.95   $8.90  
  Purchase #2 $161.78   9.337%   $176.8854   $176.89   $176.90   $176.90  
  Purchase #3 $143.41   9.200%   $156.6037   $156.60   $156.60   $156.60  
  Purchase #4 $23.30   10.263%   $25.6913   $25.69   $25.70   $25.70  
  Purchase #5 $218.99   11.103%   $243.3045   $243.30   $243.30   $243.30  
  Purchase #6 $85.30   4.557%   $89.1871   $89.19   $89.20   $89.20  
  Purchase #7 $81.79   8.742%   $88.9401   $88.94   $88.95   $88.90  
  7 purchase totals = $722.53       $789.5579   $789.56   $789.60   $789.50