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 $10.71   8.686%   $11.6403   $11.64   $11.65   $11.60  
  Purchase #2 $57.94   8.771%   $63.0219   $63.02   $63.00   $63.00  
  Purchase #3 $98.35   11.324%   $109.4872   $109.49   $109.50   $109.50  
  Purchase #4 $94.59   9.391%   $103.4729   $103.47   $103.45   $103.50  
  Purchase #5 $219.50   11.639%   $245.0476   $245.05   $245.05   $245.00  
  Purchase #6 $225.60   7.538%   $242.6057   $242.61   $242.60   $242.60  
  Purchase #7 $76.52   8.467%   $82.9989   $83.00   $83.00   $83.00  
  7 purchase totals = $783.21       $858.2745   $858.28   $858.25   $858.20