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 $87.99   5.405%   $92.7459   $92.75   $92.75   $92.70  
  Purchase #2 $81.55   4.615%   $85.3135   $85.31   $85.30   $85.30  
  Purchase #3 $34.96   4.552%   $36.5514   $36.55   $36.55   $36.60  
  Purchase #4 $76.44   10.640%   $84.5732   $84.57   $84.55   $84.60  
  Purchase #5 $226.44   9.429%   $247.791   $247.79   $247.80   $247.80  
  Purchase #6 $207.95   7.744%   $224.0536   $224.05   $224.05   $224.10  
  Purchase #7 $224.44   5.664%   $237.1523   $237.15   $237.15   $237.20  
  7 purchase totals = $939.77       $1,008.1809   $1,008.17   $1,008.15   $1,008.30