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 $204.71   10.372%   $225.9425   $225.94   $225.95   $225.90  
  Purchase #2 $173.50   11.221%   $192.9684   $192.97   $192.95   $193.00  
  Purchase #3 $151.93   6.472%   $161.7629   $161.76   $161.75   $161.80  
  Purchase #4 $28.93   11.481%   $32.2515   $32.25   $32.25   $32.30  
  Purchase #5 $161.37   13.796%   $183.6326   $183.63   $183.65   $183.60  
  Purchase #6 $46.94   5.531%   $49.5363   $49.54   $49.55   $49.50  
  Purchase #7 $241.90   9.217%   $264.1959   $264.20   $264.20   $264.20  
  7 purchase totals = $1,009.28       $1,110.2901   $1,110.29   $1,110.30   $1,110.30