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 $88.59   5.670%   $93.6131   $93.61   $93.60   $93.60  
  Purchase #2 $174.83   10.288%   $192.8165   $192.82   $192.80   $192.80  
  Purchase #3 $170.94   9.587%   $187.328   $187.33   $187.35   $187.30  
  Purchase #4 $138.76   10.106%   $152.7831   $152.78   $152.80   $152.80  
  Purchase #5 $133.89   12.815%   $151.048   $151.05   $151.05   $151.00  
  Purchase #6 $56.58   3.684%   $58.6644   $58.66   $58.65   $58.70  
  Purchase #7 $167.81   13.301%   $190.1304   $190.13   $190.15   $190.10  
  7 purchase totals = $931.40       $1,026.3835   $1,026.38   $1,026.40   $1,026.30