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 $113.47   9.694%   $124.4698   $124.47   $124.45   $124.50  
  Purchase #2 $31.29   9.190%   $34.1656   $34.17   $34.15   $34.20  
  Purchase #3 $220.51   9.756%   $242.023   $242.02   $242.00   $242.00  
  Purchase #4 $160.74   9.831%   $176.5423   $176.54   $176.55   $176.50  
  Purchase #5 $142.29   7.829%   $153.4299   $153.43   $153.45   $153.40  
  Purchase #6 $17.37   10.144%   $19.132   $19.13   $19.15   $19.10  
  Purchase #7 $195.60   11.213%   $217.5326   $217.53   $217.55   $217.50  
  7 purchase totals = $881.27       $967.2952   $967.29   $967.30   $967.20