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 $144.89   6.111%   $153.7442   $153.74   $153.75   $153.70  
  Purchase #2 $71.63   6.502%   $76.2874   $76.29   $76.30   $76.30  
  Purchase #3 $73.71   7.592%   $79.3061   $79.31   $79.30   $79.30  
  Purchase #4 $246.40   5.485%   $259.915   $259.92   $259.90   $259.90  
  Purchase #5 $198.40   3.248%   $204.844   $204.84   $204.85   $204.80  
  Purchase #6 $179.80   6.579%   $191.629   $191.63   $191.65   $191.60  
  Purchase #7 $209.72   11.157%   $233.1185   $233.12   $233.10   $233.10  
  7 purchase totals = $1,124.55       $1,198.8442   $1,198.85   $1,198.85   $1,198.70