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 $65.63   3.865%   $68.1666   $68.17   $68.15   $68.20  
  Purchase #2 $213.64   12.682%   $240.7338   $240.73   $240.75   $240.70  
  Purchase #3 $125.78   4.255%   $131.1319   $131.13   $131.15   $131.10  
  Purchase #4 $192.65   7.305%   $206.7231   $206.72   $206.70   $206.70  
  Purchase #5 $218.52   10.200%   $240.809   $240.81   $240.80   $240.80  
  Purchase #6 $165.26   10.787%   $183.0866   $183.09   $183.10   $183.10  
  Purchase #7 $191.77   9.779%   $210.5232   $210.52   $210.50   $210.50  
  7 purchase totals = $1,173.25       $1,281.1742   $1,281.17   $1,281.15   $1,281.10