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 $167.43   13.846%   $190.6124   $190.61   $190.60   $190.60  
  Purchase #2 $210.75   13.683%   $239.5869   $239.59   $239.60   $239.60  
  Purchase #3 $31.45   7.186%   $33.71   $33.71   $33.70   $33.70  
  Purchase #4 $203.78   12.507%   $229.2668   $229.27   $229.25   $229.30  
  Purchase #5 $66.74   10.274%   $73.5969   $73.60   $73.60   $73.60  
  Purchase #6 $13.96   3.498%   $14.4483   $14.45   $14.45   $14.40  
  Purchase #7 $223.30   12.677%   $251.6077   $251.61   $251.60   $251.60  
  7 purchase totals = $917.41       $1,032.8290   $1,032.84   $1,032.80   $1,032.80