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 $56.57   5.305%   $59.571   $59.57   $59.55   $59.60  
  Purchase #2 $14.25   3.858%   $14.7998   $14.80   $14.80   $14.80  
  Purchase #3 $150.29   8.819%   $163.5441   $163.54   $163.55   $163.50  
  Purchase #4 $126.84   7.119%   $135.8697   $135.87   $135.85   $135.90  
  Purchase #5 $69.80   3.633%   $72.3358   $72.34   $72.35   $72.30  
  Purchase #6 $246.26   4.488%   $257.3121   $257.31   $257.30   $257.30  
  Purchase #7 $56.95   10.461%   $62.9075   $62.91   $62.90   $62.90  
  7 purchase totals = $720.96       $766.3400   $766.34   $766.30   $766.30