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 $53.56   4.556%   $56.0002   $56.00   $56.00   $56.00  
  Purchase #2 $74.99   13.735%   $85.2899   $85.29   $85.30   $85.30  
  Purchase #3 $193.33   13.657%   $219.7331   $219.73   $219.75   $219.70  
  Purchase #4 $248.87   12.117%   $279.0256   $279.03   $279.05   $279.00  
  Purchase #5 $233.76   13.217%   $264.6561   $264.66   $264.65   $264.70  
  Purchase #6 $215.28   13.767%   $244.9176   $244.92   $244.90   $244.90  
  Purchase #7 $249.46   6.805%   $266.4358   $266.44   $266.45   $266.40  
  7 purchase totals = $1,269.25       $1,416.0583   $1,416.07   $1,416.10   $1,416.00