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 $88.55   7.862%   $95.5118   $95.51   $95.50   $95.50  
  Purchase #2 $64.94   11.244%   $72.2419   $72.24   $72.25   $72.20  
  Purchase #3 $170.71   13.423%   $193.6244   $193.62   $193.60   $193.60  
  Purchase #4 $212.92   12.432%   $239.3902   $239.39   $239.40   $239.40  
  Purchase #5 $133.94   9.845%   $147.1264   $147.13   $147.15   $147.10  
  Purchase #6 $117.85   9.443%   $128.9786   $128.98   $129.00   $129.00  
  Purchase #7 $69.74   6.695%   $74.4091   $74.41   $74.40   $74.40  
  7 purchase totals = $858.65       $951.2824   $951.28   $951.30   $951.20