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 $67.45   12.223%   $75.6944   $75.69   $75.70   $75.70  
  Purchase #2 $90.27   4.633%   $94.4522   $94.45   $94.45   $94.50  
  Purchase #3 $212.48   3.198%   $219.2751   $219.28   $219.30   $219.30  
  Purchase #4 $68.77   11.538%   $76.7047   $76.70   $76.70   $76.70  
  Purchase #5 $90.28   9.842%   $99.1654   $99.17   $99.15   $99.20  
  Purchase #6 $190.94   12.528%   $214.861   $214.86   $214.85   $214.90  
  Purchase #7 $223.65   12.310%   $251.1813   $251.18   $251.20   $251.20  
  7 purchase totals = $943.84       $1,031.3341   $1,031.33   $1,031.35   $1,031.50