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 $95.46   12.830%   $107.7075   $107.71   $107.70   $107.70  
  Purchase #2 $215.34   11.586%   $240.2893   $240.29   $240.30   $240.30  
  Purchase #3 $211.65   7.384%   $227.2782   $227.28   $227.30   $227.30  
  Purchase #4 $54.97   11.735%   $61.4207   $61.42   $61.40   $61.40  
  Purchase #5 $243.78   9.780%   $267.6217   $267.62   $267.60   $267.60  
  Purchase #6 $108.81   3.610%   $112.738   $112.74   $112.75   $112.70  
  Purchase #7 $7.42   4.427%   $7.7485   $7.75   $7.75   $7.70  
  7 purchase totals = $937.43       $1,024.8039   $1,024.81   $1,024.80   $1,024.70