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 $117.95   13.212%   $133.5336   $133.53   $133.55   $133.50  
  Purchase #2 $195.59   10.560%   $216.2443   $216.24   $216.25   $216.20  
  Purchase #3 $201.41   6.588%   $214.6789   $214.68   $214.70   $214.70  
  Purchase #4 $153.83   7.643%   $165.5872   $165.59   $165.60   $165.60  
  Purchase #5 $182.47   4.481%   $190.6465   $190.65   $190.65   $190.60  
  Purchase #6 $170.64   3.142%   $176.0015   $176.00   $176.00   $176.00  
  Purchase #7 $141.81   9.784%   $155.6847   $155.68   $155.70   $155.70  
  7 purchase totals = $1,163.70       $1,252.3767   $1,252.37   $1,252.45   $1,252.30