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 $106.68   9.542%   $116.8594   $116.86   $116.85   $116.90  
  Purchase #2 $63.35   3.118%   $65.3253   $65.33   $65.35   $65.30  
  Purchase #3 $222.37   10.552%   $245.8345   $245.83   $245.85   $245.80  
  Purchase #4 $92.85   7.617%   $99.9224   $99.92   $99.90   $99.90  
  Purchase #5 $79.50   12.530%   $89.4614   $89.46   $89.45   $89.50  
  Purchase #6 $204.98   12.376%   $230.3483   $230.35   $230.35   $230.30  
  Purchase #7 $242.99   12.774%   $274.0295   $274.03   $274.05   $274.00  
  7 purchase totals = $1,012.72       $1,121.7808   $1,121.78   $1,121.80   $1,121.70