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 $34.32   6.402%   $36.5172   $36.52   $36.50   $36.50  
  Purchase #2 $76.77   11.785%   $85.8173   $85.82   $85.80   $85.80  
  Purchase #3 $74.61   4.175%   $77.725   $77.73   $77.75   $77.70  
  Purchase #4 $218.80   3.285%   $225.9876   $225.99   $226.00   $226.00  
  Purchase #5 $200.59   8.782%   $218.2058   $218.21   $218.20   $218.20  
  Purchase #6 $229.57   4.564%   $240.0476   $240.05   $240.05   $240.00  
  Purchase #7 $149.38   6.816%   $159.5617   $159.56   $159.55   $159.60  
  7 purchase totals = $984.04       $1,043.8622   $1,043.88   $1,043.85   $1,043.80