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 $236.49   7.633%   $254.5413   $254.54   $254.55   $254.50  
  Purchase #2 $142.65   8.597%   $154.9136   $154.91   $154.90   $154.90  
  Purchase #3 $126.97   13.217%   $143.7516   $143.75   $143.75   $143.80  
  Purchase #4 $200.95   12.418%   $225.904   $225.90   $225.90   $225.90  
  Purchase #5 $93.44   8.226%   $101.1264   $101.13   $101.15   $101.10  
  Purchase #6 $96.85   10.157%   $106.6871   $106.69   $106.70   $106.70  
  Purchase #7 $44.77   8.585%   $48.6135   $48.61   $48.60   $48.60  
  7 purchase totals = $942.12       $1,035.5375   $1,035.53   $1,035.55   $1,035.50