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 $197.36   5.271%   $207.7628   $207.76   $207.75   $207.80  
  Purchase #2 $224.90   6.195%   $238.8326   $238.83   $238.85   $238.80  
  Purchase #3 $163.96   11.595%   $182.9712   $182.97   $182.95   $183.00  
  Purchase #4 $112.76   5.725%   $119.2155   $119.22   $119.20   $119.20  
  Purchase #5 $36.88   5.506%   $38.9106   $38.91   $38.90   $38.90  
  Purchase #6 $153.92   11.664%   $171.8732   $171.87   $171.85   $171.90  
  Purchase #7 $160.90   9.444%   $176.0954   $176.10   $176.10   $176.10  
  7 purchase totals = $1,050.68       $1,135.6613   $1,135.66   $1,135.60   $1,135.70