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 $209.38   11.532%   $233.5257   $233.53   $233.55   $233.50  
  Purchase #2 $226.95   12.177%   $254.5857   $254.59   $254.60   $254.60  
  Purchase #3 $192.42   7.371%   $206.6033   $206.60   $206.60   $206.60  
  Purchase #4 $179.66   5.652%   $189.8144   $189.81   $189.80   $189.80  
  Purchase #5 $245.65   12.696%   $276.8377   $276.84   $276.85   $276.80  
  Purchase #6 $57.68   5.762%   $61.0035   $61.00   $61.00   $61.00  
  Purchase #7 $76.85   11.465%   $85.6609   $85.66   $85.65   $85.70  
  7 purchase totals = $1,188.59       $1,308.0312   $1,308.03   $1,308.05   $1,308.00