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 $125.83   5.594%   $132.8689   $132.87   $132.85   $132.90  
  Purchase #2 $51.59   8.759%   $56.1088   $56.11   $56.10   $56.10  
  Purchase #3 $160.61   9.598%   $176.0253   $176.03   $176.05   $176.00  
  Purchase #4 $249.69   5.332%   $263.0035   $263.00   $263.00   $263.00  
  Purchase #5 $193.48   5.182%   $203.5061   $203.51   $203.50   $203.50  
  Purchase #6 $33.71   3.781%   $34.9846   $34.98   $35.00   $35.00  
  Purchase #7 $95.74   4.169%   $99.7314   $99.73   $99.75   $99.70  
  7 purchase totals = $910.65       $966.2286   $966.23   $966.25   $966.20