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 $245.62   11.321%   $273.4266   $273.43   $273.45   $273.40  
  Purchase #2 $54.26   4.321%   $56.6046   $56.60   $56.60   $56.60  
  Purchase #3 $230.40   10.164%   $253.8179   $253.82   $253.80   $253.80  
  Purchase #4 $55.87   9.233%   $61.0285   $61.03   $61.05   $61.00  
  Purchase #5 $113.99   11.401%   $126.986   $126.99   $127.00   $127.00  
  Purchase #6 $206.39   7.545%   $221.9621   $221.96   $221.95   $222.00  
  Purchase #7 $36.65   12.284%   $41.1521   $41.15   $41.15   $41.20  
  7 purchase totals = $943.18       $1,034.9778   $1,034.98   $1,035.00   $1,035.00