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 $60.99   7.525%   $65.5795   $65.58   $65.60   $65.60  
  Purchase #2 $149.41   6.336%   $158.8766   $158.88   $158.90   $158.90  
  Purchase #3 $94.87   12.349%   $106.5855   $106.59   $106.60   $106.60  
  Purchase #4 $72.79   12.266%   $81.7184   $81.72   $81.70   $81.70  
  Purchase #5 $120.57   6.313%   $128.1816   $128.18   $128.20   $128.20  
  Purchase #6 $169.28   13.300%   $191.7942   $191.79   $191.80   $191.80  
  Purchase #7 $212.53   12.637%   $239.3874   $239.39   $239.40   $239.40  
  7 purchase totals = $880.44       $972.1232   $972.13   $972.20   $972.20