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 $22.47   4.849%   $23.5596   $23.56   $23.55   $23.60  
  Purchase #2 $221.36   11.429%   $246.6592   $246.66   $246.65   $246.70  
  Purchase #3 $233.41   11.657%   $260.6186   $260.62   $260.60   $260.60  
  Purchase #4 $111.38   11.631%   $124.3346   $124.33   $124.35   $124.30  
  Purchase #5 $190.33   5.405%   $200.6173   $200.62   $200.60   $200.60  
  Purchase #6 $181.71   9.365%   $198.7271   $198.73   $198.75   $198.70  
  Purchase #7 $165.61   3.859%   $172.0009   $172.00   $172.00   $172.00  
  7 purchase totals = $1,126.27       $1,226.5173   $1,226.52   $1,226.50   $1,226.50