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 $244.56   5.559%   $258.1551   $258.16   $258.15   $258.20  
  Purchase #2 $250.95   7.307%   $269.2869   $269.29   $269.30   $269.30  
  Purchase #3 $167.82   5.283%   $176.6859   $176.69   $176.70   $176.70  
  Purchase #4 $218.49   13.428%   $247.8288   $247.83   $247.85   $247.80  
  Purchase #5 $161.87   9.325%   $176.9644   $176.96   $176.95   $177.00  
  Purchase #6 $165.52   8.674%   $179.8772   $179.88   $179.90   $179.90  
  Purchase #7 $46.56   10.687%   $51.5359   $51.54   $51.55   $51.50  
  7 purchase totals = $1,255.77       $1,360.3342   $1,360.35   $1,360.40   $1,360.40