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 $73.33   3.583%   $75.9574   $75.96   $75.95   $76.00  
  Purchase #2 $178.74   7.245%   $191.6897   $191.69   $191.70   $191.70  
  Purchase #3 $74.53   7.584%   $80.1824   $80.18   $80.20   $80.20  
  Purchase #4 $158.93   4.373%   $165.88   $165.88   $165.90   $165.90  
  Purchase #5 $79.97   6.624%   $85.2672   $85.27   $85.25   $85.30  
  Purchase #6 $169.85   5.375%   $178.9794   $178.98   $179.00   $179.00  
  Purchase #7 $228.81   10.662%   $253.2057   $253.21   $253.20   $253.20  
  7 purchase totals = $964.16       $1,031.1618   $1,031.17   $1,031.20   $1,031.30