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 $81.28   13.703%   $92.4178   $92.42   $92.40   $92.40  
  Purchase #2 $197.46   11.166%   $219.5084   $219.51   $219.50   $219.50  
  Purchase #3 $244.49   8.147%   $264.4086   $264.41   $264.40   $264.40  
  Purchase #4 $39.65   4.863%   $41.5782   $41.58   $41.60   $41.60  
  Purchase #5 $250.81   6.443%   $266.9697   $266.97   $266.95   $267.00  
  Purchase #6 $36.34   6.423%   $38.6741   $38.67   $38.65   $38.70  
  Purchase #7 $119.52   8.853%   $130.1011   $130.10   $130.10   $130.10  
  7 purchase totals = $969.55       $1,053.6579   $1,053.66   $1,053.60   $1,053.70