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 $114.92   9.874%   $126.2672   $126.27   $126.25   $126.30  
  Purchase #2 $53.67   7.361%   $57.6206   $57.62   $57.60   $57.60  
  Purchase #3 $246.53   12.125%   $276.4218   $276.42   $276.40   $276.40  
  Purchase #4 $108.85   9.256%   $118.9252   $118.93   $118.95   $118.90  
  Purchase #5 $43.83   3.547%   $45.3847   $45.38   $45.40   $45.40  
  Purchase #6 $217.36   13.736%   $247.2166   $247.22   $247.20   $247.20  
  Purchase #7 $115.60   9.132%   $126.1566   $126.16   $126.15   $126.20  
  7 purchase totals = $900.76       $997.9927   $998.00   $997.95   $998.00