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 $172.43   7.680%   $185.6726   $185.67   $185.65   $185.70  
  Purchase #2 $208.45   11.709%   $232.8574   $232.86   $232.85   $232.90  
  Purchase #3 $21.53   13.347%   $24.4036   $24.40   $24.40   $24.40  
  Purchase #4 $208.93   8.726%   $227.1612   $227.16   $227.15   $227.20  
  Purchase #5 $237.39   5.440%   $250.304   $250.30   $250.30   $250.30  
  Purchase #6 $7.56   6.667%   $8.064   $8.06   $8.05   $8.10  
  Purchase #7 $62.96   11.292%   $70.0694   $70.07   $70.05   $70.10  
  7 purchase totals = $919.25       $998.5322   $998.52   $998.45   $998.70