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 $43.66   12.285%   $49.0236   $49.02   $49.00   $49.00  
  Purchase #2 $176.59   8.727%   $192.001   $192.00   $192.00   $192.00  
  Purchase #3 $216.35   13.669%   $245.9229   $245.92   $245.90   $245.90  
  Purchase #4 $64.30   12.530%   $72.3568   $72.36   $72.35   $72.40  
  Purchase #5 $154.71   4.228%   $161.2511   $161.25   $161.25   $161.30  
  Purchase #6 $82.60   13.546%   $93.789   $93.79   $93.80   $93.80  
  Purchase #7 $238.54   3.609%   $247.1489   $247.15   $247.15   $247.10  
  7 purchase totals = $976.75       $1,061.4933   $1,061.49   $1,061.45   $1,061.50