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 $61.45   10.367%   $67.8205   $67.82   $67.80   $67.80  
  Purchase #2 $57.67   9.191%   $62.9704   $62.97   $62.95   $63.00  
  Purchase #3 $31.48   10.592%   $34.8144   $34.81   $34.80   $34.80  
  Purchase #4 $32.68   10.223%   $36.0209   $36.02   $36.00   $36.00  
  Purchase #5 $240.75   11.512%   $268.4651   $268.47   $268.45   $268.50  
  Purchase #6 $244.29   9.702%   $267.991   $267.99   $268.00   $268.00  
  Purchase #7 $7.62   6.600%   $8.1229   $8.12   $8.10   $8.10  
  7 purchase totals = $675.94       $746.2052   $746.20   $746.10   $746.20