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 $41.94   6.236%   $44.5554   $44.56   $44.55   $44.60  
  Purchase #2 $168.28   5.297%   $177.1938   $177.19   $177.20   $177.20  
  Purchase #3 $49.86   9.863%   $54.7777   $54.78   $54.80   $54.80  
  Purchase #4 $241.26   11.317%   $268.5634   $268.56   $268.55   $268.60  
  Purchase #5 $43.82   5.821%   $46.3708   $46.37   $46.35   $46.40  
  Purchase #6 $168.61   13.765%   $191.8192   $191.82   $191.80   $191.80  
  Purchase #7 $197.67   8.748%   $214.9622   $214.96   $214.95   $215.00  
  7 purchase totals = $911.44       $998.2425   $998.24   $998.20   $998.40