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 $68.59   3.426%   $70.9399   $70.94   $70.95   $70.90  
  Purchase #2 $10.63   6.577%   $11.3291   $11.33   $11.35   $11.30  
  Purchase #3 $231.99   13.393%   $263.0604   $263.06   $263.05   $263.10  
  Purchase #4 $79.69   3.459%   $82.4465   $82.45   $82.45   $82.40  
  Purchase #5 $160.26   9.734%   $175.8597   $175.86   $175.85   $175.90  
  Purchase #6 $118.59   12.841%   $133.8181   $133.82   $133.80   $133.80  
  Purchase #7 $228.90   13.678%   $260.2089   $260.21   $260.20   $260.20  
  7 purchase totals = $898.65       $997.6626   $997.67   $997.65   $997.60