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 $38.85   8.656%   $42.2129   $42.21   $42.20   $42.20  
  Purchase #2 $246.84   5.327%   $259.9892   $259.99   $260.00   $260.00  
  Purchase #3 $89.28   9.214%   $97.5063   $97.51   $97.50   $97.50  
  Purchase #4 $175.68   9.195%   $191.8338   $191.83   $191.85   $191.80  
  Purchase #5 $169.31   3.310%   $174.9142   $174.91   $174.90   $174.90  
  Purchase #6 $52.30   12.335%   $58.7512   $58.75   $58.75   $58.80  
  Purchase #7 $216.76   8.850%   $235.9433   $235.94   $235.95   $235.90  
  7 purchase totals = $989.02       $1,061.1509   $1,061.14   $1,061.15   $1,061.10