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 $209.58   11.480%   $233.6398   $233.64   $233.65   $233.60  
  Purchase #2 $58.58   12.376%   $65.8299   $65.83   $65.85   $65.80  
  Purchase #3 $173.27   12.372%   $194.707   $194.71   $194.70   $194.70  
  Purchase #4 $191.81   6.645%   $204.5558   $204.56   $204.55   $204.60  
  Purchase #5 $88.82   7.262%   $95.2701   $95.27   $95.25   $95.30  
  Purchase #6 $158.60   6.354%   $168.6774   $168.68   $168.70   $168.70  
  Purchase #7 $137.76   10.686%   $152.481   $152.48   $152.50   $152.50  
  7 purchase totals = $1,018.42       $1,115.1610   $1,115.17   $1,115.20   $1,115.20