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 $199.33   3.819%   $206.9424   $206.94   $206.95   $206.90  
  Purchase #2 $14.42   7.811%   $15.5463   $15.55   $15.55   $15.50  
  Purchase #3 $128.92   6.118%   $136.8073   $136.81   $136.80   $136.80  
  Purchase #4 $185.95   7.837%   $200.5229   $200.52   $200.50   $200.50  
  Purchase #5 $98.70   5.762%   $104.3871   $104.39   $104.40   $104.40  
  Purchase #6 $246.33   5.457%   $259.7722   $259.77   $259.75   $259.80  
  Purchase #7 $203.27   4.266%   $211.9415   $211.94   $211.95   $211.90  
  7 purchase totals = $1,076.92       $1,135.9197   $1,135.92   $1,135.90   $1,135.80