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 $68.71   8.166%   $74.3209   $74.32   $74.30   $74.30  
  Purchase #2 $184.35   13.556%   $209.3405   $209.34   $209.35   $209.30  
  Purchase #3 $80.46   12.694%   $90.6736   $90.67   $90.65   $90.70  
  Purchase #4 $150.73   6.577%   $160.6435   $160.64   $160.65   $160.60  
  Purchase #5 $7.93   9.168%   $8.657   $8.66   $8.65   $8.70  
  Purchase #6 $143.70   11.540%   $160.283   $160.28   $160.30   $160.30  
  Purchase #7 $86.63   8.873%   $94.3167   $94.32   $94.30   $94.30  
  7 purchase totals = $722.51       $798.2352   $798.23   $798.20   $798.20