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 $62.29   10.279%   $68.6928   $68.69   $68.70   $68.70  
  Purchase #2 $160.68   9.734%   $176.3206   $176.32   $176.30   $176.30  
  Purchase #3 $35.68   4.694%   $37.3548   $37.35   $37.35   $37.40  
  Purchase #4 $244.43   6.633%   $260.643   $260.64   $260.65   $260.60  
  Purchase #5 $132.78   4.856%   $139.2278   $139.23   $139.25   $139.20  
  Purchase #6 $229.45   9.139%   $250.4194   $250.42   $250.40   $250.40  
  Purchase #7 $114.71   8.685%   $124.6726   $124.67   $124.65   $124.70  
  7 purchase totals = $980.02       $1,057.3310   $1,057.32   $1,057.30   $1,057.30