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 $66.54   12.145%   $74.6213   $74.62   $74.60   $74.60  
  Purchase #2 $148.96   13.644%   $169.2841   $169.28   $169.30   $169.30  
  Purchase #3 $72.57   5.559%   $76.6042   $76.60   $76.60   $76.60  
  Purchase #4 $81.40   6.412%   $86.6194   $86.62   $86.60   $86.60  
  Purchase #5 $165.97   10.653%   $183.6508   $183.65   $183.65   $183.70  
  Purchase #6 $195.92   7.763%   $211.1293   $211.13   $211.15   $211.10  
  Purchase #7 $88.67   13.840%   $100.9419   $100.94   $100.95   $100.90  
  7 purchase totals = $820.03       $902.8510   $902.84   $902.85   $902.80