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 $246.89   13.869%   $281.1312   $281.13   $281.15   $281.10  
  Purchase #2 $21.76   4.172%   $22.6678   $22.67   $22.65   $22.70  
  Purchase #3 $49.25   12.838%   $55.5727   $55.57   $55.55   $55.60  
  Purchase #4 $77.61   13.164%   $87.8266   $87.83   $87.85   $87.80  
  Purchase #5 $102.83   3.252%   $106.174   $106.17   $106.15   $106.20  
  Purchase #6 $167.72   9.647%   $183.8999   $183.90   $183.90   $183.90  
  Purchase #7 $208.27   12.829%   $234.989   $234.99   $235.00   $235.00  
  7 purchase totals = $874.33       $972.2612   $972.26   $972.25   $972.30