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 $94.91   12.315%   $106.5982   $106.60   $106.60   $106.60  
  Purchase #2 $64.90   7.683%   $69.8863   $69.89   $69.90   $69.90  
  Purchase #3 $88.48   5.358%   $93.2208   $93.22   $93.20   $93.20  
  Purchase #4 $154.26   7.196%   $165.3605   $165.36   $165.35   $165.40  
  Purchase #5 $96.38   3.178%   $99.443   $99.44   $99.45   $99.40  
  Purchase #6 $250.92   12.122%   $281.3365   $281.34   $281.35   $281.30  
  Purchase #7 $201.91   4.206%   $210.4023   $210.40   $210.40   $210.40  
  7 purchase totals = $951.76       $1,026.2476   $1,026.25   $1,026.25   $1,026.20