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 $214.85   11.447%   $239.4439   $239.44   $239.45   $239.40  
  Purchase #2 $205.64   5.855%   $217.6802   $217.68   $217.70   $217.70  
  Purchase #3 $61.96   4.102%   $64.5016   $64.50   $64.50   $64.50  
  Purchase #4 $153.67   11.349%   $171.11   $171.11   $171.10   $171.10  
  Purchase #5 $247.70   11.153%   $275.326   $275.33   $275.35   $275.30  
  Purchase #6 $160.64   13.855%   $182.8967   $182.90   $182.90   $182.90  
  Purchase #7 $180.40   9.595%   $197.7094   $197.71   $197.70   $197.70  
  7 purchase totals = $1,224.86       $1,348.6678   $1,348.67   $1,348.70   $1,348.60