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 $32.27   7.764%   $34.7754   $34.78   $34.80   $34.80  
  Purchase #2 $49.98   7.448%   $53.7025   $53.70   $53.70   $53.70  
  Purchase #3 $151.58   11.275%   $168.6706   $168.67   $168.65   $168.70  
  Purchase #4 $54.37   11.843%   $60.809   $60.81   $60.80   $60.80  
  Purchase #5 $216.25   3.796%   $224.4589   $224.46   $224.45   $224.50  
  Purchase #6 $119.36   8.350%   $129.3266   $129.33   $129.35   $129.30  
  Purchase #7 $21.97   6.569%   $23.4132   $23.41   $23.40   $23.40  
  7 purchase totals = $645.78       $695.1562   $695.16   $695.15   $695.20