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 $155.98   4.597%   $163.1504   $163.15   $163.15   $163.20  
  Purchase #2 $173.39   11.750%   $193.7633   $193.76   $193.75   $193.80  
  Purchase #3 $46.35   4.162%   $48.2791   $48.28   $48.30   $48.30  
  Purchase #4 $235.99   11.624%   $263.4215   $263.42   $263.40   $263.40  
  Purchase #5 $93.65   13.344%   $106.1467   $106.15   $106.15   $106.10  
  Purchase #6 $40.83   12.248%   $45.8309   $45.83   $45.85   $45.80  
  Purchase #7 $183.54   4.597%   $191.9773   $191.98   $192.00   $192.00  
  7 purchase totals = $929.73       $1,012.5692   $1,012.57   $1,012.60   $1,012.60