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 $56.87   8.426%   $61.6619   $61.66   $61.65   $61.70  
  Purchase #2 $226.27   8.706%   $245.9691   $245.97   $245.95   $246.00  
  Purchase #3 $147.84   6.201%   $157.0076   $157.01   $157.00   $157.00  
  Purchase #4 $95.25   13.599%   $108.203   $108.20   $108.20   $108.20  
  Purchase #5 $151.52   9.229%   $165.5038   $165.50   $165.50   $165.50  
  Purchase #6 $174.62   7.595%   $187.8824   $187.88   $187.90   $187.90  
  Purchase #7 $155.68   3.705%   $161.4479   $161.45   $161.45   $161.40  
  7 purchase totals = $1,008.05       $1,087.6757   $1,087.67   $1,087.65   $1,087.70