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 $221.58   11.126%   $246.233   $246.23   $246.25   $246.20  
  Purchase #2 $93.31   3.686%   $96.7494   $96.75   $96.75   $96.70  
  Purchase #3 $42.42   6.844%   $45.3232   $45.32   $45.30   $45.30  
  Purchase #4 $208.74   9.496%   $228.562   $228.56   $228.55   $228.60  
  Purchase #5 $63.97   7.864%   $69.0006   $69.00   $69.00   $69.00  
  Purchase #6 $94.87   9.515%   $103.8969   $103.90   $103.90   $103.90  
  Purchase #7 $200.48   13.322%   $227.1879   $227.19   $227.20   $227.20  
  7 purchase totals = $925.37       $1,016.9530   $1,016.95   $1,016.95   $1,016.90