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 $63.50   3.277%   $65.5809   $65.58   $65.60   $65.60  
  Purchase #2 $148.35   8.558%   $161.0458   $161.05   $161.05   $161.00  
  Purchase #3 $75.69   9.248%   $82.6898   $82.69   $82.70   $82.70  
  Purchase #4 $18.92   6.318%   $20.1154   $20.12   $20.10   $20.10  
  Purchase #5 $215.88   5.633%   $228.0405   $228.04   $228.05   $228.00  
  Purchase #6 $42.47   7.806%   $45.7852   $45.79   $45.80   $45.80  
  Purchase #7 $118.45   4.423%   $123.689   $123.69   $123.70   $123.70  
  7 purchase totals = $683.26       $726.9466   $726.96   $727.00   $726.90