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 $62.82   9.595%   $68.8476   $68.85   $68.85   $68.80  
  Purchase #2 $141.94   8.460%   $153.9481   $153.95   $153.95   $153.90  
  Purchase #3 $147.53   5.409%   $155.5099   $155.51   $155.50   $155.50  
  Purchase #4 $178.59   3.629%   $185.071   $185.07   $185.05   $185.10  
  Purchase #5 $53.94   6.294%   $57.335   $57.34   $57.35   $57.30  
  Purchase #6 $22.98   7.278%   $24.6525   $24.65   $24.65   $24.70  
  Purchase #7 $126.73   8.819%   $137.9063   $137.91   $137.90   $137.90  
  7 purchase totals = $734.53       $783.2704   $783.28   $783.25   $783.20