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 $117.97   3.411%   $121.994   $121.99   $122.00   $122.00  
  Purchase #2 $87.98   12.153%   $98.6722   $98.67   $98.65   $98.70  
  Purchase #3 $91.48   5.759%   $96.7483   $96.75   $96.75   $96.70  
  Purchase #4 $226.47   13.871%   $257.8837   $257.88   $257.90   $257.90  
  Purchase #5 $147.89   3.636%   $153.2673   $153.27   $153.25   $153.30  
  Purchase #6 $95.58   10.249%   $105.376   $105.38   $105.40   $105.40  
  Purchase #7 $197.87   6.613%   $210.9551   $210.96   $210.95   $211.00  
  7 purchase totals = $965.24       $1,044.8966   $1,044.90   $1,044.90   $1,045.00