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 $152.59   7.371%   $163.8374   $163.84   $163.85   $163.80  
  Purchase #2 $55.33   13.284%   $62.68   $62.68   $62.70   $62.70  
  Purchase #3 $239.69   11.558%   $267.3934   $267.39   $267.40   $267.40  
  Purchase #4 $57.88   5.179%   $60.8776   $60.88   $60.90   $60.90  
  Purchase #5 $69.29   8.604%   $75.2517   $75.25   $75.25   $75.30  
  Purchase #6 $210.52   7.498%   $226.3048   $226.30   $226.30   $226.30  
  Purchase #7 $183.35   8.260%   $198.4947   $198.49   $198.50   $198.50  
  7 purchase totals = $968.65       $1,054.8396   $1,054.83   $1,054.90   $1,054.90