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 $162.26   13.371%   $183.9558   $183.96   $183.95   $184.00  
  Purchase #2 $160.65   9.679%   $176.1993   $176.20   $176.20   $176.20  
  Purchase #3 $154.44   3.595%   $159.9921   $159.99   $160.00   $160.00  
  Purchase #4 $51.35   8.707%   $55.821   $55.82   $55.80   $55.80  
  Purchase #5 $183.77   10.448%   $202.9703   $202.97   $202.95   $203.00  
  Purchase #6 $207.87   3.110%   $214.3348   $214.33   $214.35   $214.30  
  Purchase #7 $227.27   13.164%   $257.1878   $257.19   $257.20   $257.20  
  7 purchase totals = $1,147.61       $1,250.4611   $1,250.46   $1,250.45   $1,250.50