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 $62.74   6.714%   $66.9524   $66.95   $66.95   $67.00  
  Purchase #2 $41.66   3.110%   $42.9556   $42.96   $42.95   $43.00  
  Purchase #3 $105.88   5.132%   $111.3138   $111.31   $111.30   $111.30  
  Purchase #4 $132.57   12.272%   $148.839   $148.84   $148.85   $148.80  
  Purchase #5 $121.32   4.341%   $126.5865   $126.59   $126.60   $126.60  
  Purchase #6 $68.28   8.831%   $74.3098   $74.31   $74.30   $74.30  
  Purchase #7 $176.63   8.828%   $192.2229   $192.22   $192.20   $192.20  
  7 purchase totals = $709.08       $763.1800   $763.18   $763.15   $763.20