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 $28.84   4.289%   $30.0769   $30.08   $30.10   $30.10  
  Purchase #2 $158.48   13.873%   $180.4659   $180.47   $180.45   $180.50  
  Purchase #3 $13.53   9.655%   $14.8363   $14.84   $14.85   $14.80  
  Purchase #4 $123.59   13.786%   $140.6281   $140.63   $140.65   $140.60  
  Purchase #5 $18.75   10.577%   $20.7332   $20.73   $20.75   $20.70  
  Purchase #6 $10.39   4.313%   $10.8381   $10.84   $10.85   $10.80  
  Purchase #7 $114.86   12.465%   $129.1773   $129.18   $129.20   $129.20  
  7 purchase totals = $468.44       $526.7558   $526.77   $526.85   $526.70