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 $64.29   8.873%   $69.9945   $69.99   $70.00   $70.00  
  Purchase #2 $250.87   12.433%   $282.0607   $282.06   $282.05   $282.10  
  Purchase #3 $122.96   3.117%   $126.7927   $126.79   $126.80   $126.80  
  Purchase #4 $37.79   5.215%   $39.7607   $39.76   $39.75   $39.80  
  Purchase #5 $45.80   6.193%   $48.6364   $48.64   $48.65   $48.60  
  Purchase #6 $214.72   10.348%   $236.9392   $236.94   $236.95   $236.90  
  Purchase #7 $19.69   12.404%   $22.1323   $22.13   $22.15   $22.10  
  7 purchase totals = $756.12       $826.3165   $826.31   $826.35   $826.30