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 $178.51   8.834%   $194.2796   $194.28   $194.30   $194.30  
  Purchase #2 $76.90   13.433%   $87.23   $87.23   $87.25   $87.20  
  Purchase #3 $119.64   6.161%   $127.011   $127.01   $127.00   $127.00  
  Purchase #4 $238.85   3.620%   $247.4964   $247.50   $247.50   $247.50  
  Purchase #5 $112.90   8.539%   $122.5405   $122.54   $122.55   $122.50  
  Purchase #6 $69.26   10.818%   $76.7525   $76.75   $76.75   $76.80  
  Purchase #7 $165.89   6.854%   $177.2601   $177.26   $177.25   $177.30  
  7 purchase totals = $961.95       $1,032.5701   $1,032.57   $1,032.60   $1,032.60