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 $176.98   8.505%   $192.0321   $192.03   $192.05   $192.00  
  Purchase #2 $64.25   7.139%   $68.8368   $68.84   $68.85   $68.80  
  Purchase #3 $197.73   6.621%   $210.8217   $210.82   $210.80   $210.80  
  Purchase #4 $218.40   4.163%   $227.492   $227.49   $227.50   $227.50  
  Purchase #5 $29.45   13.858%   $33.5312   $33.53   $33.55   $33.50  
  Purchase #6 $102.53   8.832%   $111.5854   $111.59   $111.60   $111.60  
  Purchase #7 $164.99   9.285%   $180.3093   $180.31   $180.30   $180.30  
  7 purchase totals = $954.33       $1,024.6085   $1,024.61   $1,024.65   $1,024.50