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 $207.78   13.161%   $235.1259   $235.13   $235.15   $235.10  
  Purchase #2 $61.36   13.348%   $69.5503   $69.55   $69.55   $69.60  
  Purchase #3 $92.48   9.702%   $101.4524   $101.45   $101.45   $101.50  
  Purchase #4 $33.78   4.823%   $35.4092   $35.41   $35.40   $35.40  
  Purchase #5 $89.59   4.817%   $93.9056   $93.91   $93.90   $93.90  
  Purchase #6 $85.44   12.415%   $96.0474   $96.05   $96.05   $96.00  
  Purchase #7 $141.86   8.369%   $153.7323   $153.73   $153.75   $153.70  
  7 purchase totals = $712.29       $785.2231   $785.23   $785.25   $785.20