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 $65.34   12.377%   $73.4271   $73.43   $73.45   $73.40  
  Purchase #2 $180.67   13.725%   $205.467   $205.47   $205.45   $205.50  
  Purchase #3 $60.50   13.349%   $68.5761   $68.58   $68.60   $68.60  
  Purchase #4 $129.32   3.873%   $134.3286   $134.33   $134.35   $134.30  
  Purchase #5 $103.93   7.274%   $111.4899   $111.49   $111.50   $111.50  
  Purchase #6 $146.83   13.644%   $166.8635   $166.86   $166.85   $166.90  
  Purchase #7 $8.61   9.796%   $9.4534   $9.45   $9.45   $9.50  
  7 purchase totals = $695.20       $769.6056   $769.61   $769.65   $769.70