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 $175.70   3.522%   $181.8882   $181.89   $181.90   $181.90  
  Purchase #2 $123.86   6.224%   $131.569   $131.57   $131.55   $131.60  
  Purchase #3 $157.38   6.313%   $167.3154   $167.32   $167.30   $167.30  
  Purchase #4 $74.29   3.347%   $76.7765   $76.78   $76.80   $76.80  
  Purchase #5 $156.41   13.248%   $177.1312   $177.13   $177.15   $177.10  
  Purchase #6 $9.38   10.549%   $10.3695   $10.37   $10.35   $10.40  
  Purchase #7 $133.38   7.177%   $142.9527   $142.95   $142.95   $143.00  
  7 purchase totals = $830.40       $888.0025   $888.01   $888.00   $888.10