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 $82.82   7.216%   $88.7963   $88.80   $88.80   $88.80  
  Purchase #2 $40.66   6.781%   $43.4172   $43.42   $43.40   $43.40  
  Purchase #3 $26.38   13.446%   $29.9271   $29.93   $29.95   $29.90  
  Purchase #4 $77.32   12.132%   $86.7005   $86.70   $86.70   $86.70  
  Purchase #5 $232.64   5.229%   $244.8047   $244.80   $244.80   $244.80  
  Purchase #6 $108.51   10.560%   $119.9687   $119.97   $119.95   $120.00  
  Purchase #7 $133.55   6.481%   $142.2054   $142.21   $142.20   $142.20  
  7 purchase totals = $701.88       $755.8199   $755.83   $755.80   $755.80