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 $144.35   11.723%   $161.2722   $161.27   $161.25   $161.30  
  Purchase #2 $242.82   4.822%   $254.5288   $254.53   $254.55   $254.50  
  Purchase #3 $208.71   9.521%   $228.5813   $228.58   $228.60   $228.60  
  Purchase #4 $162.74   9.804%   $178.695   $178.70   $178.70   $178.70  
  Purchase #5 $80.95   7.774%   $87.2431   $87.24   $87.25   $87.20  
  Purchase #6 $42.68   6.703%   $45.5408   $45.54   $45.55   $45.50  
  Purchase #7 $85.40   9.204%   $93.2602   $93.26   $93.25   $93.30  
  7 purchase totals = $967.65       $1,049.1214   $1,049.12   $1,049.15   $1,049.10