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 $87.76   6.586%   $93.5399   $93.54   $93.55   $93.50  
  Purchase #2 $40.63   4.232%   $42.3495   $42.35   $42.35   $42.30  
  Purchase #3 $34.28   8.480%   $37.1869   $37.19   $37.20   $37.20  
  Purchase #4 $209.54   4.786%   $219.5686   $219.57   $219.55   $219.60  
  Purchase #5 $115.32   4.270%   $120.2442   $120.24   $120.25   $120.20  
  Purchase #6 $31.54   3.507%   $32.6461   $32.65   $32.65   $32.60  
  Purchase #7 $216.64   10.660%   $239.7338   $239.73   $239.75   $239.70  
  7 purchase totals = $735.71       $785.2690   $785.27   $785.30   $785.10