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 $221.92   5.726%   $234.6271   $234.63   $234.65   $234.60  
  Purchase #2 $88.69   3.709%   $91.9795   $91.98   $92.00   $92.00  
  Purchase #3 $188.39   5.527%   $198.8023   $198.80   $198.80   $198.80  
  Purchase #4 $110.66   9.247%   $120.8927   $120.89   $120.90   $120.90  
  Purchase #5 $166.98   11.562%   $186.2862   $186.29   $186.30   $186.30  
  Purchase #6 $233.38   8.290%   $252.7272   $252.73   $252.75   $252.70  
  Purchase #7 $198.51   7.533%   $213.4638   $213.46   $213.45   $213.50  
  7 purchase totals = $1,208.53       $1,298.7788   $1,298.78   $1,298.85   $1,298.80