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 $248.57   8.207%   $268.9701   $268.97   $268.95   $269.00  
  Purchase #2 $95.77   3.133%   $98.7705   $98.77   $98.75   $98.80  
  Purchase #3 $168.55   12.851%   $190.2104   $190.21   $190.20   $190.20  
  Purchase #4 $48.73   3.795%   $50.5793   $50.58   $50.60   $50.60  
  Purchase #5 $207.44   5.807%   $219.486   $219.49   $219.50   $219.50  
  Purchase #6 $94.39   11.607%   $105.3458   $105.35   $105.35   $105.30  
  Purchase #7 $178.30   12.873%   $201.2526   $201.25   $201.25   $201.30  
  7 purchase totals = $1,041.75       $1,134.6147   $1,134.62   $1,134.60   $1,134.70