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 $128.37   10.542%   $141.9028   $141.90   $141.90   $141.90  
  Purchase #2 $75.93   8.119%   $82.0948   $82.09   $82.10   $82.10  
  Purchase #3 $18.94   5.495%   $19.9808   $19.98   $20.00   $20.00  
  Purchase #4 $66.26   7.550%   $71.2626   $71.26   $71.25   $71.30  
  Purchase #5 $34.80   6.268%   $36.9813   $36.98   $37.00   $37.00  
  Purchase #6 $211.73   6.823%   $226.1763   $226.18   $226.20   $226.20  
  Purchase #7 $208.26   5.157%   $219   $219.00   $219.00   $219.00  
  7 purchase totals = $744.29       $797.3986   $797.39   $797.45   $797.50