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 $65.97   7.526%   $70.9349   $70.93   $70.95   $70.90  
  Purchase #2 $10.80   8.353%   $11.7021   $11.70   $11.70   $11.70  
  Purchase #3 $207.86   9.348%   $227.2908   $227.29   $227.30   $227.30  
  Purchase #4 $191.86   8.513%   $208.193   $208.19   $208.20   $208.20  
  Purchase #5 $170.27   12.378%   $191.346   $191.35   $191.35   $191.30  
  Purchase #6 $88.62   13.237%   $100.3506   $100.35   $100.35   $100.40  
  Purchase #7 $224.65   12.369%   $252.437   $252.44   $252.45   $252.40  
  7 purchase totals = $960.03       $1,062.2544   $1,062.25   $1,062.30   $1,062.20