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 $122.32   3.833%   $127.0085   $127.01   $127.00   $127.00  
  Purchase #2 $145.88   3.242%   $150.6094   $150.61   $150.60   $150.60  
  Purchase #3 $250.33   7.765%   $269.7681   $269.77   $269.75   $269.80  
  Purchase #4 $164.28   5.444%   $173.2234   $173.22   $173.20   $173.20  
  Purchase #5 $36.95   7.370%   $39.6732   $39.67   $39.65   $39.70  
  Purchase #6 $119.69   11.722%   $133.7201   $133.72   $133.70   $133.70  
  Purchase #7 $101.62   8.844%   $110.6073   $110.61   $110.60   $110.60  
  7 purchase totals = $941.07       $1,004.6100   $1,004.61   $1,004.50   $1,004.60