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 $246.83   8.652%   $268.1857   $268.19   $268.20   $268.20  
  Purchase #2 $220.54   4.526%   $230.5216   $230.52   $230.50   $230.50  
  Purchase #3 $190.88   8.393%   $206.9006   $206.90   $206.90   $206.90  
  Purchase #4 $160.72   5.154%   $169.0035   $169.00   $169.00   $169.00  
  Purchase #5 $26.97   8.208%   $29.1837   $29.18   $29.20   $29.20  
  Purchase #6 $103.86   11.812%   $116.1279   $116.13   $116.15   $116.10  
  Purchase #7 $46.48   7.305%   $49.8754   $49.88   $49.90   $49.90  
  7 purchase totals = $996.28       $1,069.7984   $1,069.80   $1,069.85   $1,069.80