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 $117.46   8.275%   $127.1798   $127.18   $127.20   $127.20  
  Purchase #2 $107.89   7.362%   $115.8329   $115.83   $115.85   $115.80  
  Purchase #3 $88.93   8.574%   $96.5549   $96.55   $96.55   $96.60  
  Purchase #4 $247.76   8.650%   $269.1912   $269.19   $269.20   $269.20  
  Purchase #5 $249.50   10.659%   $276.0942   $276.09   $276.10   $276.10  
  Purchase #6 $197.63   11.285%   $219.9325   $219.93   $219.95   $219.90  
  Purchase #7 $108.89   12.765%   $122.7898   $122.79   $122.80   $122.80  
  7 purchase totals = $1,118.06       $1,227.5753   $1,227.56   $1,227.65   $1,227.60