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 $148.92   8.268%   $161.2327   $161.23   $161.25   $161.20  
  Purchase #2 $44.89   9.226%   $49.0316   $49.03   $49.05   $49.00  
  Purchase #3 $211.83   7.711%   $228.1642   $228.16   $228.15   $228.20  
  Purchase #4 $242.61   9.451%   $265.5391   $265.54   $265.55   $265.50  
  Purchase #5 $83.35   9.778%   $91.5   $91.50   $91.50   $91.50  
  Purchase #6 $67.74   8.793%   $73.6964   $73.70   $73.70   $73.70  
  Purchase #7 $238.89   11.779%   $267.0289   $267.03   $267.05   $267.00  
  7 purchase totals = $1,038.23       $1,136.1929   $1,136.19   $1,136.25   $1,136.10