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 $84.83   13.147%   $95.9826   $95.98   $96.00   $96.00  
  Purchase #2 $222.93   6.505%   $237.4316   $237.43   $237.45   $237.40  
  Purchase #3 $14.82   9.133%   $16.1735   $16.17   $16.15   $16.20  
  Purchase #4 $32.37   8.778%   $35.2114   $35.21   $35.20   $35.20  
  Purchase #5 $140.46   3.549%   $145.4449   $145.44   $145.45   $145.40  
  Purchase #6 $232.46   3.746%   $241.168   $241.17   $241.15   $241.20  
  Purchase #7 $58.46   13.448%   $66.3217   $66.32   $66.30   $66.30  
  7 purchase totals = $786.33       $837.7337   $837.72   $837.70   $837.70