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 $192.66   5.279%   $202.8305   $202.83   $202.85   $202.80  
  Purchase #2 $77.47   13.633%   $88.0315   $88.03   $88.05   $88.00  
  Purchase #3 $20.65   9.202%   $22.5502   $22.55   $22.55   $22.60  
  Purchase #4 $166.73   8.125%   $180.2768   $180.28   $180.30   $180.30  
  Purchase #5 $56.79   6.846%   $60.6778   $60.68   $60.70   $60.70  
  Purchase #6 $205.83   7.810%   $221.9053   $221.91   $221.90   $221.90  
  Purchase #7 $217.26   4.730%   $227.5364   $227.54   $227.55   $227.50  
  7 purchase totals = $937.39       $1,003.8085   $1,003.82   $1,003.90   $1,003.80