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 $70.58   3.535%   $73.075   $73.08   $73.10   $73.10  
  Purchase #2 $72.81   10.344%   $80.3415   $80.34   $80.35   $80.30  
  Purchase #3 $81.47   12.355%   $91.5356   $91.54   $91.55   $91.50  
  Purchase #4 $213.68   4.783%   $223.9003   $223.90   $223.90   $223.90  
  Purchase #5 $75.62   8.874%   $82.3305   $82.33   $82.35   $82.30  
  Purchase #6 $73.76   3.644%   $76.4478   $76.45   $76.45   $76.40  
  Purchase #7 $236.44   3.861%   $245.5689   $245.57   $245.55   $245.60  
  7 purchase totals = $824.36       $873.1996   $873.21   $873.25   $873.10