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 $89.72   4.727%   $93.9611   $93.96   $93.95   $94.00  
  Purchase #2 $208.36   12.791%   $235.0113   $235.01   $235.00   $235.00  
  Purchase #3 $232.37   5.108%   $244.2395   $244.24   $244.25   $244.20  
  Purchase #4 $207.82   5.538%   $219.3291   $219.33   $219.35   $219.30  
  Purchase #5 $35.34   4.206%   $36.8264   $36.83   $36.85   $36.80  
  Purchase #6 $62.41   6.477%   $66.4523   $66.45   $66.45   $66.50  
  Purchase #7 $14.48   7.362%   $15.546   $15.55   $15.55   $15.50  
  7 purchase totals = $850.50       $911.3657   $911.37   $911.40   $911.30