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 $60.91   12.343%   $68.4281   $68.43   $68.45   $68.40  
  Purchase #2 $79.46   10.350%   $87.6841   $87.68   $87.70   $87.70  
  Purchase #3 $22.75   10.277%   $25.088   $25.09   $25.10   $25.10  
  Purchase #4 $234.64   11.556%   $261.755   $261.76   $261.75   $261.80  
  Purchase #5 $241.93   9.252%   $264.3134   $264.31   $264.30   $264.30  
  Purchase #6 $196.74   4.351%   $205.3002   $205.30   $205.30   $205.30  
  Purchase #7 $233.52   6.681%   $249.1215   $249.12   $249.10   $249.10  
  7 purchase totals = $1,069.95       $1,161.6903   $1,161.69   $1,161.70   $1,161.70