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 $204.39   10.708%   $226.2761   $226.28   $226.30   $226.30  
  Purchase #2 $205.28   11.309%   $228.4951   $228.50   $228.50   $228.50  
  Purchase #3 $57.74   6.511%   $61.4995   $61.50   $61.50   $61.50  
  Purchase #4 $133.82   6.193%   $142.1075   $142.11   $142.10   $142.10  
  Purchase #5 $169.87   9.200%   $185.498   $185.50   $185.50   $185.50  
  Purchase #6 $31.66   3.647%   $32.8146   $32.81   $32.80   $32.80  
  Purchase #7 $224.38   12.785%   $253.067   $253.07   $253.05   $253.10  
  7 purchase totals = $1,027.14       $1,129.7578   $1,129.77   $1,129.75   $1,129.80