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 $141.68   13.864%   $161.3225   $161.32   $161.30   $161.30  
  Purchase #2 $138.69   9.228%   $151.4883   $151.49   $151.50   $151.50  
  Purchase #3 $68.78   4.477%   $71.8593   $71.86   $71.85   $71.90  
  Purchase #4 $236.68   13.865%   $269.4957   $269.50   $269.50   $269.50  
  Purchase #5 $217.50   12.609%   $244.9246   $244.92   $244.90   $244.90  
  Purchase #6 $75.51   7.409%   $81.1045   $81.10   $81.10   $81.10  
  Purchase #7 $202.93   6.308%   $215.7308   $215.73   $215.75   $215.70  
  7 purchase totals = $1,081.77       $1,195.9257   $1,195.92   $1,195.90   $1,195.90