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 $209.84   7.865%   $226.3439   $226.34   $226.35   $226.30  
  Purchase #2 $247.83   6.871%   $264.8584   $264.86   $264.85   $264.90  
  Purchase #3 $131.75   8.175%   $142.5206   $142.52   $142.50   $142.50  
  Purchase #4 $96.31   10.860%   $106.7693   $106.77   $106.75   $106.80  
  Purchase #5 $225.36   8.742%   $245.061   $245.06   $245.05   $245.10  
  Purchase #6 $129.70   6.546%   $138.1902   $138.19   $138.20   $138.20  
  Purchase #7 $116.63   13.176%   $131.9972   $132.00   $132.00   $132.00  
  7 purchase totals = $1,157.42       $1,255.7406   $1,255.74   $1,255.70   $1,255.80