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 $50.68   5.673%   $53.5551   $53.56   $53.55   $53.60  
  Purchase #2 $58.67   4.233%   $61.1535   $61.15   $61.15   $61.20  
  Purchase #3 $119.46   12.268%   $134.1154   $134.12   $134.10   $134.10  
  Purchase #4 $233.56   12.302%   $262.2926   $262.29   $262.30   $262.30  
  Purchase #5 $150.32   3.452%   $155.509   $155.51   $155.50   $155.50  
  Purchase #6 $27.68   4.679%   $28.9751   $28.98   $29.00   $29.00  
  Purchase #7 $167.47   6.504%   $178.3622   $178.36   $178.35   $178.40  
  7 purchase totals = $807.84       $873.9629   $873.97   $873.95   $874.10