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 $85.66   3.858%   $88.9648   $88.96   $88.95   $89.00  
  Purchase #2 $177.43   3.311%   $183.3047   $183.30   $183.30   $183.30  
  Purchase #3 $180.85   11.179%   $201.0672   $201.07   $201.05   $201.10  
  Purchase #4 $198.72   7.454%   $213.5326   $213.53   $213.55   $213.50  
  Purchase #5 $167.42   3.635%   $173.5057   $173.51   $173.50   $173.50  
  Purchase #6 $235.59   12.864%   $265.8963   $265.90   $265.90   $265.90  
  Purchase #7 $63.80   4.375%   $66.5913   $66.59   $66.60   $66.60  
  7 purchase totals = $1,109.47       $1,192.8626   $1,192.86   $1,192.85   $1,192.90