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 $200.85   12.397%   $225.7494   $225.75   $225.75   $225.70  
  Purchase #2 $121.57   3.633%   $125.9866   $125.99   $126.00   $126.00  
  Purchase #3 $191.27   13.415%   $216.9289   $216.93   $216.95   $216.90  
  Purchase #4 $16.58   3.588%   $17.1749   $17.17   $17.15   $17.20  
  Purchase #5 $158.75   7.545%   $170.7277   $170.73   $170.75   $170.70  
  Purchase #6 $54.93   12.273%   $61.6716   $61.67   $61.65   $61.70  
  Purchase #7 $215.64   9.339%   $235.7786   $235.78   $235.80   $235.80  
  7 purchase totals = $959.59       $1,054.0177   $1,054.02   $1,054.05   $1,054.00