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 $184.37   4.418%   $192.5155   $192.52   $192.50   $192.50  
  Purchase #2 $84.66   13.356%   $95.9672   $95.97   $95.95   $96.00  
  Purchase #3 $141.95   7.458%   $152.5366   $152.54   $152.55   $152.50  
  Purchase #4 $220.66   11.398%   $245.8108   $245.81   $245.80   $245.80  
  Purchase #5 $91.64   10.465%   $101.2301   $101.23   $101.25   $101.20  
  Purchase #6 $165.88   13.224%   $187.816   $187.82   $187.80   $187.80  
  Purchase #7 $74.64   6.601%   $79.567   $79.57   $79.55   $79.60  
  7 purchase totals = $963.80       $1,055.4432   $1,055.46   $1,055.40   $1,055.40