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 $214.25   5.736%   $226.5394   $226.54   $226.55   $226.50  
  Purchase #2 $151.76   13.151%   $171.718   $171.72   $171.70   $171.70  
  Purchase #3 $74.76   11.649%   $83.4688   $83.47   $83.45   $83.50  
  Purchase #4 $187.67   7.556%   $201.8503   $201.85   $201.85   $201.90  
  Purchase #5 $44.49   12.107%   $49.8764   $49.88   $49.90   $49.90  
  Purchase #6 $204.98   4.201%   $213.5912   $213.59   $213.60   $213.60  
  Purchase #7 $62.44   5.194%   $65.6831   $65.68   $65.70   $65.70  
  7 purchase totals = $940.35       $1,012.7272   $1,012.73   $1,012.75   $1,012.80