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 $140.66   9.413%   $153.9003   $153.90   $153.90   $153.90  
  Purchase #2 $63.97   4.222%   $66.6708   $66.67   $66.65   $66.70  
  Purchase #3 $250.57   7.110%   $268.3855   $268.39   $268.40   $268.40  
  Purchase #4 $28.50   7.557%   $30.6537   $30.65   $30.65   $30.70  
  Purchase #5 $211.65   4.513%   $221.2018   $221.20   $221.20   $221.20  
  Purchase #6 $228.92   13.258%   $259.2702   $259.27   $259.25   $259.30  
  Purchase #7 $211.51   11.729%   $236.318   $236.32   $236.30   $236.30  
  7 purchase totals = $1,135.78       $1,236.4003   $1,236.40   $1,236.35   $1,236.50