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 $78.39   12.558%   $88.2342   $88.23   $88.25   $88.20  
  Purchase #2 $227.38   8.121%   $245.8455   $245.85   $245.85   $245.80  
  Purchase #3 $8.91   4.468%   $9.3081   $9.31   $9.30   $9.30  
  Purchase #4 $58.73   4.369%   $61.2959   $61.30   $61.30   $61.30  
  Purchase #5 $246.42   9.615%   $270.1133   $270.11   $270.10   $270.10  
  Purchase #6 $82.41   3.187%   $85.0364   $85.04   $85.05   $85.00  
  Purchase #7 $40.64   7.394%   $43.6449   $43.64   $43.65   $43.60  
  7 purchase totals = $742.88       $803.4783   $803.48   $803.50   $803.30