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 $193.27   10.134%   $212.856   $212.86   $212.85   $212.90  
  Purchase #2 $64.64   11.246%   $71.9094   $71.91   $71.90   $71.90  
  Purchase #3 $243.54   6.225%   $258.7004   $258.70   $258.70   $258.70  
  Purchase #4 $161.94   7.321%   $173.7956   $173.80   $173.80   $173.80  
  Purchase #5 $192.68   9.635%   $211.2447   $211.24   $211.25   $211.20  
  Purchase #6 $111.68   7.411%   $119.9566   $119.96   $119.95   $120.00  
  Purchase #7 $208.58   6.824%   $222.8135   $222.81   $222.80   $222.80  
  7 purchase totals = $1,176.33       $1,271.2762   $1,271.28   $1,271.25   $1,271.30