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 $95.40   11.860%   $106.7144   $106.71   $106.70   $106.70  
  Purchase #2 $52.86   3.494%   $54.7069   $54.71   $54.70   $54.70  
  Purchase #3 $153.98   3.130%   $158.7996   $158.80   $158.80   $158.80  
  Purchase #4 $64.60   8.835%   $70.3074   $70.31   $70.30   $70.30  
  Purchase #5 $111.44   9.556%   $122.0892   $122.09   $122.10   $122.10  
  Purchase #6 $210.67   5.729%   $222.7393   $222.74   $222.75   $222.70  
  Purchase #7 $75.69   7.503%   $81.369   $81.37   $81.35   $81.40  
  7 purchase totals = $764.64       $816.7258   $816.73   $816.70   $816.70