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 $182.81   11.773%   $204.3322   $204.33   $204.35   $204.30  
  Purchase #2 $103.43   4.611%   $108.1992   $108.20   $108.20   $108.20  
  Purchase #3 $185.46   3.491%   $191.9344   $191.93   $191.95   $191.90  
  Purchase #4 $189.34   3.257%   $195.5068   $195.51   $195.50   $195.50  
  Purchase #5 $164.79   9.457%   $180.3742   $180.37   $180.35   $180.40  
  Purchase #6 $26.45   9.846%   $29.0543   $29.05   $29.05   $29.10  
  Purchase #7 $230.29   4.336%   $240.2754   $240.28   $240.30   $240.30  
  7 purchase totals = $1,082.57       $1,149.6765   $1,149.67   $1,149.70   $1,149.70