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 $149.63   10.706%   $165.6494   $165.65   $165.65   $165.60  
  Purchase #2 $223.64   9.152%   $244.1075   $244.11   $244.10   $244.10  
  Purchase #3 $44.72   6.587%   $47.6657   $47.67   $47.65   $47.70  
  Purchase #4 $246.80   6.477%   $262.7852   $262.79   $262.80   $262.80  
  Purchase #5 $15.57   4.690%   $16.3002   $16.30   $16.30   $16.30  
  Purchase #6 $177.72   5.665%   $187.7878   $187.79   $187.80   $187.80  
  Purchase #7 $79.50   11.159%   $88.3714   $88.37   $88.35   $88.40  
  7 purchase totals = $937.58       $1,012.6672   $1,012.68   $1,012.65   $1,012.70