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 $212.96   10.397%   $235.1015   $235.10   $235.10   $235.10  
  Purchase #2 $240.28   10.125%   $264.6084   $264.61   $264.60   $264.60  
  Purchase #3 $12.98   4.323%   $13.5411   $13.54   $13.55   $13.50  
  Purchase #4 $226.31   11.429%   $252.175   $252.18   $252.20   $252.20  
  Purchase #5 $206.51   12.139%   $231.5782   $231.58   $231.60   $231.60  
  Purchase #6 $197.26   13.833%   $224.547   $224.55   $224.55   $224.50  
  Purchase #7 $49.78   7.410%   $53.4687   $53.47   $53.45   $53.50  
  7 purchase totals = $1,146.08       $1,275.0199   $1,275.03   $1,275.05   $1,275.00