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 $212.47   11.556%   $237.023   $237.02   $237.00   $237.00  
  Purchase #2 $38.33   7.397%   $41.1653   $41.17   $41.15   $41.20  
  Purchase #3 $99.61   7.305%   $106.8865   $106.89   $106.90   $106.90  
  Purchase #4 $106.57   11.530%   $118.8575   $118.86   $118.85   $118.90  
  Purchase #5 $242.39   13.321%   $274.6788   $274.68   $274.70   $274.70  
  Purchase #6 $201.48   3.174%   $207.875   $207.88   $207.90   $207.90  
  Purchase #7 $37.99   8.516%   $41.2252   $41.23   $41.25   $41.20  
  7 purchase totals = $938.84       $1,027.7113   $1,027.73   $1,027.75   $1,027.80