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 $95.59   11.838%   $106.9059   $106.91   $106.90   $106.90  
  Purchase #2 $238.50   3.453%   $246.7354   $246.74   $246.75   $246.70  
  Purchase #3 $74.28   4.648%   $77.7325   $77.73   $77.75   $77.70  
  Purchase #4 $12.72   8.162%   $13.7582   $13.76   $13.75   $13.80  
  Purchase #5 $102.96   10.658%   $113.9335   $113.93   $113.95   $113.90  
  Purchase #6 $108.53   8.273%   $117.5087   $117.51   $117.50   $117.50  
  Purchase #7 $45.39   8.522%   $49.2581   $49.26   $49.25   $49.30  
  7 purchase totals = $677.97       $725.8323   $725.84   $725.85   $725.80