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 $141.36   8.201%   $152.9529   $152.95   $152.95   $153.00  
  Purchase #2 $82.70   13.195%   $93.6123   $93.61   $93.60   $93.60  
  Purchase #3 $46.71   13.643%   $53.0826   $53.08   $53.10   $53.10  
  Purchase #4 $218.30   4.851%   $228.8897   $228.89   $228.90   $228.90  
  Purchase #5 $37.93   5.596%   $40.0526   $40.05   $40.05   $40.10  
  Purchase #6 $169.69   4.473%   $177.2802   $177.28   $177.30   $177.30  
  Purchase #7 $10.55   5.511%   $11.1314   $11.13   $11.15   $11.10  
  7 purchase totals = $707.24       $757.0017   $756.99   $757.05   $757.10