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 $152.88   6.814%   $163.2972   $163.30   $163.30   $163.30  
  Purchase #2 $127.95   10.872%   $141.8607   $141.86   $141.85   $141.90  
  Purchase #3 $149.64   7.634%   $161.0635   $161.06   $161.05   $161.10  
  Purchase #4 $211.25   8.151%   $228.469   $228.47   $228.45   $228.50  
  Purchase #5 $55.42   10.103%   $61.0191   $61.02   $61.00   $61.00  
  Purchase #6 $209.26   12.599%   $235.6247   $235.62   $235.60   $235.60  
  Purchase #7 $176.62   3.601%   $182.9801   $182.98   $183.00   $183.00  
  7 purchase totals = $1,083.02       $1,174.3143   $1,174.31   $1,174.25   $1,174.40