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 $54.67   5.788%   $57.8343   $57.83   $57.85   $57.80  
  Purchase #2 $25.28   11.284%   $28.1326   $28.13   $28.15   $28.10  
  Purchase #3 $82.80   6.246%   $87.9717   $87.97   $87.95   $88.00  
  Purchase #4 $54.25   12.638%   $61.1061   $61.11   $61.10   $61.10  
  Purchase #5 $201.49   8.735%   $219.0902   $219.09   $219.10   $219.10  
  Purchase #6 $237.53   9.292%   $259.6013   $259.60   $259.60   $259.60  
  Purchase #7 $7.59   12.609%   $8.547   $8.55   $8.55   $8.50  
  7 purchase totals = $663.61       $722.2832   $722.28   $722.30   $722.20