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 $244.97   11.764%   $273.7883   $273.79   $273.80   $273.80  
  Purchase #2 $155.40   12.115%   $174.2267   $174.23   $174.25   $174.20  
  Purchase #3 $47.94   4.669%   $50.1783   $50.18   $50.20   $50.20  
  Purchase #4 $202.85   9.138%   $221.3864   $221.39   $221.40   $221.40  
  Purchase #5 $203.50   13.617%   $231.2106   $231.21   $231.20   $231.20  
  Purchase #6 $185.97   12.736%   $209.6551   $209.66   $209.65   $209.70  
  Purchase #7 $246.45   3.798%   $255.8102   $255.81   $255.80   $255.80  
  7 purchase totals = $1,287.08       $1,416.2556   $1,416.27   $1,416.30   $1,416.30