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 $181.57   8.622%   $197.225   $197.23   $197.25   $197.20  
  Purchase #2 $68.87   8.857%   $74.9698   $74.97   $74.95   $75.00  
  Purchase #3 $230.33   8.622%   $250.1891   $250.19   $250.20   $250.20  
  Purchase #4 $202.46   11.312%   $225.3623   $225.36   $225.35   $225.40  
  Purchase #5 $174.96   6.492%   $186.3184   $186.32   $186.30   $186.30  
  Purchase #6 $211.52   10.578%   $233.8946   $233.89   $233.90   $233.90  
  Purchase #7 $159.90   11.329%   $178.0151   $178.02   $178.00   $178.00  
  7 purchase totals = $1,229.61       $1,345.9743   $1,345.98   $1,345.95   $1,346.00