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 $183.83   4.802%   $192.6575   $192.66   $192.65   $192.70  
  Purchase #2 $149.69   8.699%   $162.7115   $162.71   $162.70   $162.70  
  Purchase #3 $125.89   8.494%   $136.5831   $136.58   $136.60   $136.60  
  Purchase #4 $163.54   10.305%   $180.3928   $180.39   $180.40   $180.40  
  Purchase #5 $24.33   10.301%   $26.8362   $26.84   $26.85   $26.80  
  Purchase #6 $195.40   8.754%   $212.5053   $212.51   $212.50   $212.50  
  Purchase #7 $179.58   12.369%   $201.7923   $201.79   $201.80   $201.80  
  7 purchase totals = $1,022.26       $1,113.4787   $1,113.48   $1,113.50   $1,113.50