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 $238.70   11.226%   $265.4965   $265.50   $265.50   $265.50  
  Purchase #2 $62.68   9.353%   $68.5425   $68.54   $68.55   $68.50  
  Purchase #3 $78.90   6.557%   $84.0735   $84.07   $84.05   $84.10  
  Purchase #4 $21.96   4.570%   $22.9636   $22.96   $22.95   $23.00  
  Purchase #5 $79.30   4.561%   $82.9169   $82.92   $82.90   $82.90  
  Purchase #6 $21.64   11.697%   $24.1712   $24.17   $24.15   $24.20  
  Purchase #7 $219.74   3.668%   $227.8001   $227.80   $227.80   $227.80  
  7 purchase totals = $722.92       $775.9643   $775.96   $775.90   $776.00