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 $212.51   6.828%   $227.0202   $227.02   $227.00   $227.00  
  Purchase #2 $228.65   11.655%   $255.2992   $255.30   $255.30   $255.30  
  Purchase #3 $98.75   10.844%   $109.4585   $109.46   $109.45   $109.50  
  Purchase #4 $162.44   9.196%   $177.378   $177.38   $177.40   $177.40  
  Purchase #5 $85.49   7.749%   $92.1146   $92.11   $92.10   $92.10  
  Purchase #6 $73.95   9.681%   $81.1091   $81.11   $81.10   $81.10  
  Purchase #7 $69.52   9.327%   $76.0041   $76.00   $76.00   $76.00  
  7 purchase totals = $931.31       $1,018.3837   $1,018.38   $1,018.35   $1,018.40