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 $176.64   8.192%   $191.1103   $191.11   $191.10   $191.10  
  Purchase #2 $24.33   4.588%   $25.4463   $25.45   $25.45   $25.40  
  Purchase #3 $89.70   5.704%   $94.8165   $94.82   $94.80   $94.80  
  Purchase #4 $90.69   8.551%   $98.4449   $98.44   $98.45   $98.40  
  Purchase #5 $196.55   13.509%   $223.1019   $223.10   $223.10   $223.10  
  Purchase #6 $216.88   13.764%   $246.7314   $246.73   $246.75   $246.70  
  Purchase #7 $32.49   8.416%   $35.2244   $35.22   $35.20   $35.20  
  7 purchase totals = $827.28       $914.8757   $914.87   $914.85   $914.70