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 $237.28   11.743%   $265.1438   $265.14   $265.15   $265.10  
  Purchase #2 $123.97   6.749%   $132.3367   $132.34   $132.35   $132.30  
  Purchase #3 $141.56   3.687%   $146.7793   $146.78   $146.80   $146.80  
  Purchase #4 $190.76   9.440%   $208.7677   $208.77   $208.75   $208.80  
  Purchase #5 $103.60   3.491%   $107.2167   $107.22   $107.20   $107.20  
  Purchase #6 $135.57   12.434%   $152.4268   $152.43   $152.45   $152.40  
  Purchase #7 $90.87   5.773%   $96.1159   $96.12   $96.10   $96.10  
  7 purchase totals = $1,023.61       $1,108.7869   $1,108.80   $1,108.80   $1,108.70