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 $246.51   12.160%   $276.4856   $276.49   $276.50   $276.50  
  Purchase #2 $40.43   12.735%   $45.5788   $45.58   $45.60   $45.60  
  Purchase #3 $227.74   12.556%   $256.335   $256.34   $256.35   $256.30  
  Purchase #4 $84.74   9.308%   $92.6276   $92.63   $92.65   $92.60  
  Purchase #5 $72.37   13.186%   $81.9127   $81.91   $81.90   $81.90  
  Purchase #6 $103.59   11.845%   $115.8602   $115.86   $115.85   $115.90  
  Purchase #7 $97.80   8.143%   $105.7639   $105.76   $105.75   $105.80  
  7 purchase totals = $873.18       $974.5638   $974.57   $974.60   $974.60