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 $128.37   12.435%   $144.3328   $144.33   $144.35   $144.30  
  Purchase #2 $214.32   5.606%   $226.3348   $226.33   $226.35   $226.30  
  Purchase #3 $175.98   3.822%   $182.706   $182.71   $182.70   $182.70  
  Purchase #4 $23.68   5.463%   $24.9736   $24.97   $24.95   $25.00  
  Purchase #5 $91.86   6.244%   $97.5957   $97.60   $97.60   $97.60  
  Purchase #6 $175.51   4.863%   $184.0451   $184.05   $184.05   $184.00  
  Purchase #7 $151.69   9.806%   $166.5647   $166.56   $166.55   $166.60  
  7 purchase totals = $961.41       $1,026.5527   $1,026.55   $1,026.55   $1,026.50