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 $34.93   10.359%   $38.5484   $38.55   $38.55   $38.50  
  Purchase #2 $188.73   7.212%   $202.3412   $202.34   $202.35   $202.30  
  Purchase #3 $75.99   11.664%   $84.8535   $84.85   $84.85   $84.90  
  Purchase #4 $165.77   7.832%   $178.7531   $178.75   $178.75   $178.80  
  Purchase #5 $158.28   10.445%   $174.8123   $174.81   $174.80   $174.80  
  Purchase #6 $53.54   11.325%   $59.6034   $59.60   $59.60   $59.60  
  Purchase #7 $75.74   9.689%   $83.0784   $83.08   $83.10   $83.10  
  7 purchase totals = $752.98       $821.9903   $821.98   $822.00   $822.00