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 $38.71   6.579%   $41.2567   $41.26   $41.25   $41.30  
  Purchase #2 $241.65   11.833%   $270.2444   $270.24   $270.25   $270.20  
  Purchase #3 $123.59   10.521%   $136.5929   $136.59   $136.60   $136.60  
  Purchase #4 $25.74   5.729%   $27.2146   $27.21   $27.20   $27.20  
  Purchase #5 $234.47   5.335%   $246.979   $246.98   $247.00   $247.00  
  Purchase #6 $170.77   8.189%   $184.7544   $184.75   $184.75   $184.80  
  Purchase #7 $205.33   5.493%   $216.6088   $216.61   $216.60   $216.60  
  7 purchase totals = $1,040.26       $1,123.6508   $1,123.64   $1,123.65   $1,123.70