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 $70.76   6.124%   $75.0933   $75.09   $75.10   $75.10  
  Purchase #2 $228.80   6.534%   $243.7498   $243.75   $243.75   $243.70  
  Purchase #3 $40.31   3.622%   $41.77   $41.77   $41.75   $41.80  
  Purchase #4 $95.74   5.210%   $100.7281   $100.73   $100.75   $100.70  
  Purchase #5 $184.86   10.505%   $204.2795   $204.28   $204.30   $204.30  
  Purchase #6 $54.25   8.757%   $59.0007   $59.00   $59.00   $59.00  
  Purchase #7 $237.55   8.585%   $257.9437   $257.94   $257.95   $257.90  
  7 purchase totals = $912.27       $982.5651   $982.56   $982.60   $982.50