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 $192.95   7.494%   $207.4097   $207.41   $207.40   $207.40  
  Purchase #2 $180.42   10.765%   $199.8422   $199.84   $199.85   $199.80  
  Purchase #3 $95.95   8.469%   $104.076   $104.08   $104.10   $104.10  
  Purchase #4 $158.56   6.619%   $169.0551   $169.06   $169.05   $169.10  
  Purchase #5 $30.85   12.129%   $34.5918   $34.59   $34.60   $34.60  
  Purchase #6 $161.42   9.286%   $176.4095   $176.41   $176.40   $176.40  
  Purchase #7 $39.35   4.799%   $41.2384   $41.24   $41.25   $41.20  
  7 purchase totals = $859.50       $932.6227   $932.63   $932.65   $932.60