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 $234.36   8.402%   $254.0509   $254.05   $254.05   $254.10  
  Purchase #2 $247.44   11.796%   $276.628   $276.63   $276.65   $276.60  
  Purchase #3 $38.39   8.575%   $41.6819   $41.68   $41.70   $41.70  
  Purchase #4 $88.86   12.357%   $99.8404   $99.84   $99.85   $99.80  
  Purchase #5 $217.30   8.339%   $235.4206   $235.42   $235.40   $235.40  
  Purchase #6 $81.92   5.188%   $86.17   $86.17   $86.15   $86.20  
  Purchase #7 $148.28   4.872%   $155.5042   $155.50   $155.50   $155.50  
  7 purchase totals = $1,056.55       $1,149.2960   $1,149.29   $1,149.30   $1,149.30