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 $21.65   4.293%   $22.5794   $22.58   $22.60   $22.60  
  Purchase #2 $9.41   5.736%   $9.9498   $9.95   $9.95   $9.90  
  Purchase #3 $213.32   8.447%   $231.3391   $231.34   $231.35   $231.30  
  Purchase #4 $144.26   12.676%   $162.5464   $162.55   $162.55   $162.50  
  Purchase #5 $250.73   3.801%   $260.2602   $260.26   $260.25   $260.30  
  Purchase #6 $37.32   12.701%   $42.06   $42.06   $42.05   $42.10  
  Purchase #7 $26.52   4.497%   $27.7126   $27.71   $27.70   $27.70  
  7 purchase totals = $703.21       $756.4475   $756.45   $756.45   $756.40