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 $250.63   12.459%   $281.856   $281.86   $281.85   $281.90  
  Purchase #2 $25.70   12.458%   $28.9017   $28.90   $28.90   $28.90  
  Purchase #3 $165.61   10.657%   $183.2591   $183.26   $183.25   $183.30  
  Purchase #4 $112.98   4.207%   $117.7331   $117.73   $117.75   $117.70  
  Purchase #5 $154.55   5.246%   $162.6577   $162.66   $162.65   $162.70  
  Purchase #6 $99.68   6.859%   $106.5171   $106.52   $106.50   $106.50  
  Purchase #7 $186.71   3.514%   $193.271   $193.27   $193.25   $193.30  
  7 purchase totals = $995.86       $1,074.1957   $1,074.20   $1,074.15   $1,074.30