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 $208.76   7.609%   $224.6445   $224.64   $224.65   $224.60  
  Purchase #2 $40.31   13.493%   $45.749   $45.75   $45.75   $45.70  
  Purchase #3 $147.56   3.620%   $152.9017   $152.90   $152.90   $152.90  
  Purchase #4 $44.40   10.421%   $49.0269   $49.03   $49.05   $49.00  
  Purchase #5 $189.54   8.387%   $205.4367   $205.44   $205.45   $205.40  
  Purchase #6 $223.54   10.512%   $247.0385   $247.04   $247.05   $247.00  
  Purchase #7 $101.97   7.467%   $109.5841   $109.58   $109.60   $109.60  
  7 purchase totals = $956.08       $1,034.3814   $1,034.38   $1,034.45   $1,034.20