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 $42.42   5.193%   $44.6229   $44.62   $44.60   $44.60  
  Purchase #2 $205.41   7.206%   $220.2118   $220.21   $220.20   $220.20  
  Purchase #3 $6.52   12.512%   $7.3358   $7.34   $7.35   $7.30  
  Purchase #4 $55.93   7.530%   $60.1415   $60.14   $60.15   $60.10  
  Purchase #5 $250.67   7.583%   $269.6783   $269.68   $269.70   $269.70  
  Purchase #6 $208.52   7.684%   $224.5427   $224.54   $224.55   $224.50  
  Purchase #7 $176.75   11.349%   $196.8094   $196.81   $196.80   $196.80  
  7 purchase totals = $946.22       $1,023.3424   $1,023.34   $1,023.35   $1,023.20