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 $58.26   3.455%   $60.2729   $60.27   $60.25   $60.30  
  Purchase #2 $166.96   9.406%   $182.6643   $182.66   $182.65   $182.70  
  Purchase #3 $87.41   4.787%   $91.5943   $91.59   $91.60   $91.60  
  Purchase #4 $14.79   4.300%   $15.426   $15.43   $15.45   $15.40  
  Purchase #5 $105.69   12.192%   $118.5757   $118.58   $118.60   $118.60  
  Purchase #6 $81.47   9.609%   $89.2985   $89.30   $89.30   $89.30  
  Purchase #7 $32.49   5.656%   $34.3276   $34.33   $34.35   $34.30  
  7 purchase totals = $547.07       $592.1593   $592.16   $592.20   $592.20