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 $82.42   8.349%   $89.3012   $89.30   $89.30   $89.30  
  Purchase #2 $44.58   10.649%   $49.3273   $49.33   $49.35   $49.30  
  Purchase #3 $220.65   8.548%   $239.5112   $239.51   $239.50   $239.50  
  Purchase #4 $131.75   10.254%   $145.2596   $145.26   $145.25   $145.30  
  Purchase #5 $155.71   7.786%   $167.8336   $167.83   $167.85   $167.80  
  Purchase #6 $50.84   9.249%   $55.5422   $55.54   $55.55   $55.50  
  Purchase #7 $242.26   10.448%   $267.5713   $267.57   $267.55   $267.60  
  7 purchase totals = $928.21       $1,014.3464   $1,014.34   $1,014.35   $1,014.30