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 $110.84   7.631%   $119.2982   $119.30   $119.30   $119.30  
  Purchase #2 $58.80   3.831%   $61.0526   $61.05   $61.05   $61.10  
  Purchase #3 $96.90   5.808%   $102.528   $102.53   $102.55   $102.50  
  Purchase #4 $112.59   10.765%   $124.7103   $124.71   $124.70   $124.70  
  Purchase #5 $61.55   8.746%   $66.9332   $66.93   $66.95   $66.90  
  Purchase #6 $215.94   6.525%   $230.0301   $230.03   $230.05   $230.00  
  Purchase #7 $234.97   4.828%   $246.3144   $246.31   $246.30   $246.30  
  7 purchase totals = $891.59       $950.8668   $950.86   $950.90   $950.80