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 $205.93   10.508%   $227.5691   $227.57   $227.55   $227.60  
  Purchase #2 $247.82   10.131%   $272.9266   $272.93   $272.95   $272.90  
  Purchase #3 $23.37   5.295%   $24.6074   $24.61   $24.60   $24.60  
  Purchase #4 $27.90   4.809%   $29.2417   $29.24   $29.25   $29.20  
  Purchase #5 $128.60   11.142%   $142.9286   $142.93   $142.95   $142.90  
  Purchase #6 $181.55   11.775%   $202.9275   $202.93   $202.95   $202.90  
  Purchase #7 $98.65   13.526%   $111.9934   $111.99   $112.00   $112.00  
  7 purchase totals = $913.82       $1,012.1943   $1,012.20   $1,012.25   $1,012.10