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 $171.29   8.554%   $185.9421   $185.94   $185.95   $185.90  
  Purchase #2 $118.68   5.572%   $125.2928   $125.29   $125.30   $125.30  
  Purchase #3 $9.29   8.818%   $10.1092   $10.11   $10.10   $10.10  
  Purchase #4 $215.93   4.624%   $225.9146   $225.91   $225.90   $225.90  
  Purchase #5 $228.85   13.397%   $259.509   $259.51   $259.50   $259.50  
  Purchase #6 $119.92   6.518%   $127.7364   $127.74   $127.75   $127.70  
  Purchase #7 $232.69   9.299%   $254.3278   $254.33   $254.35   $254.30  
  7 purchase totals = $1,096.65       $1,188.8319   $1,188.83   $1,188.85   $1,188.70