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 $93.67   7.495%   $100.6906   $100.69   $100.70   $100.70  
  Purchase #2 $60.72   4.761%   $63.6109   $63.61   $63.60   $63.60  
  Purchase #3 $136.86   4.629%   $143.1952   $143.20   $143.20   $143.20  
  Purchase #4 $173.32   5.393%   $182.6671   $182.67   $182.65   $182.70  
  Purchase #5 $10.60   4.871%   $11.1163   $11.12   $11.10   $11.10  
  Purchase #6 $39.37   3.423%   $40.7176   $40.72   $40.70   $40.70  
  Purchase #7 $183.72   11.605%   $205.0407   $205.04   $205.05   $205.00  
  7 purchase totals = $698.26       $747.0384   $747.05   $747.00   $747.00