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 $119.84   3.279%   $123.7696   $123.77   $123.75   $123.80  
  Purchase #2 $246.37   6.749%   $262.9975   $263.00   $263.00   $263.00  
  Purchase #3 $141.47   8.768%   $153.8741   $153.87   $153.85   $153.90  
  Purchase #4 $41.41   13.317%   $46.9246   $46.92   $46.90   $46.90  
  Purchase #5 $99.28   10.786%   $109.9883   $109.99   $110.00   $110.00  
  Purchase #6 $25.41   3.183%   $26.2188   $26.22   $26.20   $26.20  
  Purchase #7 $176.60   4.513%   $184.57   $184.57   $184.55   $184.60  
  7 purchase totals = $850.38       $908.3429   $908.34   $908.25   $908.40