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 $169.71   11.256%   $188.8126   $188.81   $188.80   $188.80  
  Purchase #2 $236.69   5.699%   $250.179   $250.18   $250.20   $250.20  
  Purchase #3 $220.79   10.296%   $243.5225   $243.52   $243.50   $243.50  
  Purchase #4 $30.75   12.541%   $34.6064   $34.61   $34.60   $34.60  
  Purchase #5 $201.29   7.380%   $216.1452   $216.15   $216.15   $216.10  
  Purchase #6 $73.86   12.540%   $83.122   $83.12   $83.10   $83.10  
  Purchase #7 $15.98   5.586%   $16.8726   $16.87   $16.85   $16.90  
  7 purchase totals = $949.07       $1,033.2603   $1,033.26   $1,033.20   $1,033.20