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 $59.51   7.431%   $63.9322   $63.93   $63.95   $63.90  
  Purchase #2 $66.47   6.212%   $70.5991   $70.60   $70.60   $70.60  
  Purchase #3 $153.62   8.254%   $166.2998   $166.30   $166.30   $166.30  
  Purchase #4 $227.83   3.564%   $235.9499   $235.95   $235.95   $235.90  
  Purchase #5 $205.47   6.749%   $219.3372   $219.34   $219.35   $219.30  
  Purchase #6 $220.31   12.493%   $247.8333   $247.83   $247.85   $247.80  
  Purchase #7 $243.84   5.768%   $257.9047   $257.90   $257.90   $257.90  
  7 purchase totals = $1,177.05       $1,261.8562   $1,261.85   $1,261.90   $1,261.70