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 $66.35   10.784%   $73.5052   $73.51   $73.50   $73.50  
  Purchase #2 $22.52   12.612%   $25.3602   $25.36   $25.35   $25.40  
  Purchase #3 $156.62   11.474%   $174.5906   $174.59   $174.60   $174.60  
  Purchase #4 $18.58   10.583%   $20.5463   $20.55   $20.55   $20.50  
  Purchase #5 $115.48   5.601%   $121.948   $121.95   $121.95   $121.90  
  Purchase #6 $132.76   4.562%   $138.8165   $138.82   $138.80   $138.80  
  Purchase #7 $220.42   12.636%   $248.2723   $248.27   $248.25   $248.30  
  7 purchase totals = $732.73       $803.0391   $803.05   $803.00   $803.00