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 $39.71   8.401%   $43.046   $43.05   $43.05   $43.00  
  Purchase #2 $48.65   7.342%   $52.2219   $52.22   $52.20   $52.20  
  Purchase #3 $125.73   5.303%   $132.3975   $132.40   $132.40   $132.40  
  Purchase #4 $226.61   6.543%   $241.4371   $241.44   $241.45   $241.40  
  Purchase #5 $192.72   13.242%   $218.24   $218.24   $218.25   $218.20  
  Purchase #6 $31.96   13.177%   $36.1714   $36.17   $36.15   $36.20  
  Purchase #7 $54.45   11.685%   $60.8125   $60.81   $60.80   $60.80  
  7 purchase totals = $719.83       $784.3264   $784.33   $784.30   $784.20